I remember counting down to my twelfth birthday because my mum had told me that I'd be able to babysit her friend's children - three boys: 2, 4 and 7 - and be paid £10. By 13, I was babysitting every Friday and Saturday 7pm till late, for 4 families, sometimes for two sets of children at once.
This is why 'childcare' isn't offered for 12 year olds. For decades, in the absence of relevant special needs (worth noting here: I'm autistic and was the most capable carer in my friendship group), children this age have been considered unrequiring of physical adult supervision. There isn't any basis to think this has changed.
I can understand that you don't want to leave your son for long periods throughout the week. However, I think that's more to do with quality of life than a need for supervision for its own sake.
There are loads of parents where I live (rurally) who are present, but completely skint and unable to do much/go anywhere with their kids during the holidays. Therefore, there's an argument for more, and more accessible, provision for all kids.
I'd personally make this argument at the same time as avoiding references to childcare/supervision etc. It's a small difference, but it helps people focus on the real issue. He's not going to melt like a snowflake because he's on his own, but he'd have a much better time if there was something sociable and enriching for him to do that you could access and afford.
This provision should be within the government's remit, especially considering the rise in mental health difficulties within the adolescent population. It would be prudent for them to ensure older kids weren't being isolated for long periods.
Otherwise, you'll just get lots of people (like me) telling you that they were "working down t'mines at his age!" 