When people talk about helmet requirements, or laws, or requiring them for children, it is almost always done without any reference to the odds involved, and how riding style and activity impacts risk.
Tossing a helmet in the trash doubles your risk. Taking up jumping increases it 20-100 times. It is illogical to require helmets for children, either by rule or by law, and yet allow them to jump with horses.
The odds of a western rider having a head injury while wearing a cowboy hat is only a small fraction of the odds a jump rider faces while wearing a helmet and any other protective gear one can think of wearing. A law that requires helmets but allows jumping is stupid, but then, I think most lawmakers are far to ignorant to have any business passing any restrictions on horses and riding.
Having seen these studies, if I knew a kid who wanted to take up jumping, I'd strongly encourage them to take up dressage or western riding first, and learn jumping when they were old enough to accept the risk. And being 52, I wouldn't be surprised when they ignored me!
And when I ride in a western or Australian saddle? I'll wear a helmet. I've spent a fair bit of time recently dealing with a screaming 6 month old granddaughter who explodes when Mommy isn't present, and I dearly want to live long enough to see HER
dealing with a screaming 6 month old monster...
Oldest daughter on the left, holding my son's baby - the screamer. Daughter-in-law on the right, holding oldest daughter's QUIET baby. Very quiet Australian Shepherd looking up at the bottom.
...Your groom is holding him and attempting to hold your top hat and helmet at the same time while you fix your hair (imagine you're a chick for a second)...
While both are a huge leap, imagining I'm a chick is probably easier than imagining me as a competent dressage rider - and I'm sure Mia would agree! Or are there old, slouching, chubby bifocal wearing dressage riders who bounce like a sack of potatoes in the saddle?