Thank you for all your brilliant suggestions and advice.
I have no influence over his parents’ choice of school or high school. His father attends Mass with him, but his mother is not a Catholic and has recently begun to point out all the ‘flaws’ (in her opinion) in the Catholic Church’s teachings - which is not helpful to say the least.
I think he would benefit much more from listening to the readings, Gospel and sermon than skipping off to Children’s Liturgy which lasts from after the Opening Prayer to the start of the Offertory. For him, Children’s Liturgy is a chance to be indulged by the leaders, who constantly tell him all his questions are wonderful and his knowledge is amazing. To be fair, he does ask some intelligent questions and he does retain information well and can apply it - sensibly when he chooses, or to deliberately provoke a response too. What he lacks is self control and empathy with others in the group.
For example, this Sunday, we had a brilliant sermon, that he would have enjoyed. The Priest explained that the Quoran had over 100 different names for God, which translated to descriptions like ‘mighty, powerful, all-knowing etc.,’ but only the Christian faith refered to a humble God (a God who 'humbled himself to be born …etc)
I love the idea of a Latin Mass

It could go either way: he’ll either be mesmerised, or be grateful for the English Mass, where he can at least understand what is being said