I did see some older children with long thick hair get baptised the same way, for them I would be certain the water didn't touch their skin.
Even that's a tough one ... where the only way that really could happen would be if their heads were tilted and the water just made a glancing blow off the hair, or else they had some incredibly tough hair spray.
SOME water is going to make it through to the skin in nearly all cases.
... again, except the glancing blow scenario, which I have actually seen once, where a thick-headed teenager had his head turn sideways and the water just coursed off the back of his thick hair.
Why are the new generations of priests so stupid? They hardly educate them on some of the most basic things. Yeah, I'm sure they have all kinds of lessons on how to do counseling of drug addicts or whatnot ... thing which are better left to professionals (with Catholic faith).