the helmet I had initially ordered in size S for my 10 months old son. I had measured the head circumference and came to 48 cm. The XS-helmet was but then a little bit too small. The next size (S, from 50 cm) fits now like a glove, helmet wobbles not on the head and the adjustment range is still a lot in there. What really convinced me is the lightweight - most children weigh as much as adult helmets helmets and are simply unreasonable difficult for children. I have never found one that is lighter than the Casco Mini Pro Racer :-)
