Size is always the biggest problem when it comes to fitting something on the body. Everyone has a different shape and size of the head, so fitting is an issue. The same helmet and size will be too big for some and too small for others, so it may take a couple of returns to get the perfect one. Combined with the fact that kids’ heads are still growing, sizing for a helmet can be difficult. Most of the manufacturers give sizing and measuring instructions. If these are followed precisely, you should have fewer problems with getting a helmet that is not right.