How much does it really matter to have a carrier that fits from one kneepit to the other? Read on for a discussion of this topic that moves beyond the knee to knee.

Quite a few people visit  my sling library on the lookout for toddler carriers, as their little ones are “no longer knee to knee” in the sling that they have, and asking me what comes next!
In Sheffield the problem arises particularly in relation to Sleepy Nico baby carriers, which are very well loved here. People are reluctant to move into other carriers that may not feel so comfy,, but don’t wish to hurt their children or be unsafe by using a sling that may be too small, or moving to a “toddler size” that may actually be too big!. There is a lot of conflicting information on the internet about the sizing of carriers which many people find very confusing to navigate….


1) What is knee to knee?

Knee to knee simply means that the carrier you are using supports your child across the full width of both thighs, from one knee to the other, reaching into the knee pit. This ensures a comfortable seat for your child, more like sitting in a hammock, than perching on a stool. The diagram below shows a carrier that is reaching knee to knee, and the side on view shows how this will create a comfortable seat.healthy hips hip dysplasia slings

Having the knees raised above bottom also increases flexibility at the hip joint and makes it easier to flex and extend. Try it yourself! Sit astride a chair, facing the back. See how easy it is to shuffle forwards, keeping your legs flat on the chair seat, to get your symphysis pubis (the front pelvic bone) to touch the back of the chair. Those of us with lovely flexible hips who can do the Buddha position easily will find this a doddle, but others of us will find it a little sore as the ligaments get strained. You can release this tension instantly by bringing your knees up above the level of your bottom, and this will often tuck your pelvis inwards, bringing a little curve to the base of your spine. This position you have created is called the M shape, for obvious reasons, and is the ideal position, supported knee to knee with bottom a little lower. There are a few circumstances where this standard recommendation may not be appropriate, and more care will need to be taken, such as children with hyperextension conditions, or achondroplasia for a start. If you are at all unsure, do see your local sling and carrier consultant or ask for advice from trained professionals. We are always happy to help with tailored advice! For more information if a narrow based carrier will harm your child’s hips, see my “Healthy Hips” article.

2) What if my carrier seems to be no longer knee to knee?

There are usually several factors to consider here, depending on the age of your child.

Firstly, is your young child sitting in the M shape, with their bottom sitting deeply in the panel, and knees raised up with pelvis tilted? This often makes a big difference to how young children sit in carriers, and you may find it instantly makes things more comfortable for you and your child, especially if the panel has also previously felt too short. It is worth taking your time over positioning your child really well and may extend the life of your carrier for some time.

Older children who can stand and walk do not need the same level of support and will be fine if the carrier offers them good thigh support. It should keep them in a comfy seated position with lower legs bent at the knee, at right angles is fine. Older children have more muscle strength and co-ordination, and can help to grip on, so they do not need full knee to knee. They need more space and freedom to move, and will want to get down more often anyway! In this photo the sling is not reaching to the kneepit but to mid-thigh. Just make sure there is no digging in of the fabric along the thigh, and no pinning of knees with wrap fabric passes.

Secondly, is your child central in the carrier? I find that people have a tendency to hold their children slightly off centre when in arms, and then bring the panel up from that place so the child remains in a similar off-centre position. This will mean that one leg is less well supported than the other, and can lead to leaning and discomfort. Keeping a child central will often improve comfort both for your child, and for you.

Thirdly, is your child comfortable or not? Older children may be able to tell you, but for younger ones, our role as parent is to be caring and careful, and aware of non-verbal communication. Sling users usually worry (in the early stages with small babies) about over-spreading hips, as babies cry when they are uncomfortable, and children vary in their hip flexibility. This is why many carriers are “cinched” in when they are too big. Always listen to your child. If they are comfortable, and happily able to move their legs at the knee, and legs do not seem to be dragging down but are well supported, you may not need to size up just yet.

Fourthly, is your child growing taller as well? This may be more of a problem than the width of a sling if a child has a very long body and is able lean back too far from a panel that is too short. If your child leans back too far they may unbalance you. Keeping yourself and your child safe is more important than being knee to knee.

If your child is happy in their current carrier, that is good news. If they are not, and legs seem to be dangling unsupported in more of an A shape, or they are able to lean back, it may be time to consider another, bigger carrier. It might help to look in the mirror to assess your child’s leg position and how much back support they have.

3) Is it unsafe to use a carrier that is too small?

It depends on the child, and the parent! As I have pointed out in my Healthy Hips article, there is little evidence that a “narrow” seat will be harmful to any child beyond the age of six months, and even before then, the risk is low. So an older child, especially when they can bear their own weight on their legs, is not at risk of damage from not being perfectly knee to knee. They may not be as comfy as they could be if the carrier is very small and they end up with legs dangling in an A shape (this could be tiring for a child, and lead to red marks on the inside of the thighs). Let your child be your guide. I usually suggest that a carrier that supports at least to mid-thigh and allows a comfy seat with knees at right angles or a little less for older children, is fine to use.

Many big brand carriers such as Beco, Boba, Ergo and Manduca to name just a few, say that their carriers are safe to use well into toddlerhood, long after some people would feel their babies were too big for them (they are all formally safety tested). Sometimes it can seem that people are in a hurry to move out of a “standard” size carrier, before it is really necessary. Again, check your positioning, and do get some help from your local sling consultant/peer supporter/library/sling meet if you are unsure. One size does not fit all, some babies are big, some toddlers are small, some parents find bigger carriers more comfy for them, some parents find smaller carriers work better for their frames. Each carrier has its own specifications too. Some are narrow, some are short-panelled, some are wide, some are tall, some have buckles that insert very low and can squash baby thighs, etc. It is all dependent on the individual situation, and what works for one baby and parent may not work for another. Skill levels vary too, as does child compliance – a contented baby may be happy for the parent to take the time to maximise positioning, others may resist.

If you have a half buckle, or a meh dai, there are ways to tie the shoulder straps to come beneath the child’s knee, to further extend the width of the support offered by the panel itself.

4) Is it unsafe to use a carrier that is too large?

This is a more complex issue. The crucial issue to consider is child safety, based on the ABC and the TICKS guidelines. A child should not be invisible inside a carrier that is too tall, as this could be a risk to their airway and their breathing. This is one reason why many carriers have inserts, to raise children higher up the panel so their faces are visible at all times and chin can be kept off chest. I would rather see a child that was in a carrier slightly too short in the body, than in one that has too tall a panel.

As for the width and knee to knee… here is a photo to illustrate the difference. A carrier that is too wide will make a child’s legs stick out straight, or he will strain against the fabric to bend his knee (which may lead to red marks, even if no voiced complaint at the time). He may feel some strain at his inner thigh if he cannot bend his knee in this hip-extended position (see the chair illustration above). Sometimes it can be suggested that the panel could be “cinched in” with something like a webbing belt, or a ribbon, etc and this may, if there is no alternative, make the carrier much more comfy as he is now able to bend his knee in the M shape. However, this will invalidate the warranty of the carrier and place strain at the waistband.

Also, by bringing the knees up higher, the angle that the hips need to open at the groin is reduced, as the joint is able to rotate more easily. *Please note that this is a hack that is rarely recommended ; if it is not in the instructions it will invalidate any warranty.*


Every parent, child and carrier combination is individual, and needs assessing as such. Many carriers that are not knee to knee may well be able to be used for your child for longer than you might expect, so there may not need to be a great rush to size up. Buying new carriers for many is great fun – if you are going to buy something too big for your child to grow into, do ensure it is comfortable for them, and not too tall. You may have more time in your current carrier than you think, to give you time to find the next carrier (if needed).

But what about the Superman Sleepy Nico at the start? Is it OK?  I think we can all agree that the little SuperBaby will be OK to enjoy his special carrier for a while longer yet.