So basically children of the very rich and children of the unemployed get a summer holiday and every one else ( dare I use the phrase the squeezed middle) stays in school.
I have no issue with holiday activities being run in schools for school children, at my own school we run lots of such activities and my children have attended them. I just have an issue with it being linked so closely to teachers. If the odd teacher wants to offer their services - and it would IMO be the odd teacher- that is fine but do not present it as something that is closely linked with teachers .
I also would like to know where the money comes from . When my children attend summer camp style things in the local secondary schools, it costs around £25 a day. As you seem to think this would be used by so many parents that could be £25k worth of child are a day being given away. ( My school has 1500 student so assuming that 2\3 take up the offer) .
I have a responsibility for behaviour at my school, I will not be choosing to work an extra six weeks for no pay. On a daily basis in my job, I am working with very challenging parents, social workers, mental health professionals. Thinking about the pastoral team that I work with, they mostly have young families and so would not want to work over the optional six weeks. They tend to be well paid so even if you offered them more money they probably would ot come in. I would imagine that many of the very challenging families that I work with will not be keeping their children at home for six weeks, so they will be coming into school. There will be a six week block when these families will not have access to the senior member of staff that they are used to working with. More importantly these rather vulnerable children will also have to get used to a different pastoral head, possibly a different form tutor and subject teachers. It is not a huge issue, when you take on board the fact that you are quite graciously giviing away millions of pounds worth of free childcare but as someone who specializes in pastoral care and child protection it would worry me.
I do think that you have a point about very vulnerable children being at home for six weeks in very dire circumstances and I think that some kind of summer camp would be great for them . However I think it would be most valuable if they were to experience something completely different from school , to broaden their horizons rather than give them the same old thing but with unpredictable staffing.