My kid is 3.5 y.o. head size 52cm. I find the Youth version (7-10) or adult small size fits better.

Great helmet. Bought it in light purple for my daughter and she loves it. I should have bought the LED one; sometimes we come out at night and it is extremely helpful.

Great build quality. Was a it small but that is on me and I will gladly do an exchange. One of the best feeling kids helmets I have seen.

Well made, great fit. Exactly what you’d expect from specialized. I feel great knowing that if the kiddo has a spill, her melon will be protected.

My son is 6 with a 52 cm diameter and this helmet barely fits. The problem with it seems to me is that the shell is too narrow on the sides. I don't think he'll be able to wear it very long.

My kids head is 53 cm. Helmet sizing range says 50-55 on the box or ages 4-7. This helmet doesn't even come close to fitting.