Claudius last year we had 30 kids to train each week so we had to tell everyone to bring a ball. You wouldn't know what they'd turn up with, usually the cheapest, heaviest crap their parents could get because they kept losing them. This year I have 11 players and the club gave me 8 balls at the correct weights for their age group. Makes a huge difference. I don't put much focus on heading with the group because its not hugely necessary but I don't ban it either and I do like to practice crossing and set pieces which leads to some heading. At 9 years old very few are good at it though. I've one guy who's a real threat on corners and another couple who are capable of getting a head on it. One of them is my own son because I did work on heading with him.
I was talking about this story with a friend earlier who's son also plays and a decent enough level by Irish standards. He was recently on a tour to Liverpool and Manchester with his U13 team and they hammered Steven Gerrards academy team. The academy coach couldn't believe it, said they almost never lose. Apparently even this really high level youth team in Liverpool looked completely at sea when the ball was in the air but the Irish lads were well able for it.
In my opinion I don't think its that big a deal for young players to head an appropriately weighted ball every now and then. The issues comes from repetitive focus on it. I remember Keown talking about it and mentioning he'd have to head hundreds of balls per session. I think when thats happening you can develop issues.
Clrnc especially if it's off the top of my head
poor technique is giving you headaches 😉