My 2-yo daughter has no problem keeping her helmet on. However putting it on is tough. She finds it ticklish each time me or my wife tries to put it on. But once it's on, she's ok with it.
We tried to have her look up pointing to a bird or plane. That way her chin will face up. However that window of opportunity is only a few seconds. Any strategy to put helmet on a child who thinks it's a ticklish game?