Re head strength. I think this will vary a lot form child to child.This can be increased immensely by swimming from an early age. Just a thought. Also baby wearing/carrying, homebirths /natural births and waterbirths and letting baby root around for the breast.My daughter for example has never been in a stroller and has swam since she was 5 months old so her neck strength is way stronger than average.Not to say it is or isn't strong enough for a helmet at one (she is 2 now so it's long past) but something to consider;-)
She now has the sit on the handle bars seat and loves it. Also just started her on her own balance bike.