@NameChangeAgainAgainAgainAgain - it sounds like your son is a bright boy, so I am sure he is aware of how much you and your dh struggle - so he is (possibly) going into this with his eyes wide open - that's a good thing.
My parents were both teachers (though mum went on to being a Youth Employment Officer, and stopped work when my sister and I came along), and my middle son is a teacher, and I know how much work it is - but I also know how rewarding it can be - as I am sure you do too. Honestly, knowing ds2 as well as I know him, I am sure he has picked the right career, and I am proud of him.
It is pretty early days yet - if I were you, I'd be encouraging your son to look at degree courses that would lead him towards a career in PE, rather than a specific teaching degree, because that will give him more flexibility in the future - if he does something sports science based, he will be able to go on and do the PGCE if he wants to, but he'd also have other careers open to him.
Would it be possible for him to do any volunteering in classrooms, while he is still at school? At ds2's senior school, the top years were encouraged to help out as assistants in some classes, and the prefects were expected to be available, on a rota, in the dining room for younger kids to come and ask for help with their school work. Ds2 also got involved in drama and sports - not just participating but helping to organise - all of which gave him more understanding of what teaching involved. To be honest, when I saw how much he threw himself into all aspects of school life, and took on responsibility, that was what made me think that teaching might be a good career for him.
He did a maths degree - and whilst teaching was in his mind as one possible career, it was by no means the only thing he considered - but when he graduated, he had used the four years of his degree to narrow down his choices, and he decided to do the PGCE.