It's reactionary, do-goody crap that Alex Salmond is sadly quite likely to go along with, having already proved himself as the chief whip of the nanny state in Scotland.
Because children are actually pretty good at making their own judgements on this sort of thing, in my experience, most of them would rather wear helmets than not anyway. I can definitely understand that ski schools would require young learners to wear helmets because of insurance requirements and it's insurance companies sadly that are likely to be the reason why helmets will become compulsory rather than because of any law (except Salmond). I can see the day in the not too distant future when snowsports insurance for overseas travel requires helmets to be worn on penalty of a 'head injury' clause if not.
On a moral and safety ground though, there is no more justification for people (young or old) to be forced to wear helmets on the snow than there is when skateboarding or cycling and a legal enforcement would be a sad thing. Don't go along with it Mr Salmond !!
As you know though Alan, I am a lidhead myself and so are my children so although I'd hate to see it pass into compulsion, I still don't understand why you are so determined to put up frivolous arguments against their benefits.