These conversations always go down the same route. The issues with a lack of childcare options and teacher working conditions are the least important question to ask.
Do you want schools to open for more weeks because you want your children to have more time learning? The best educational models in the world (Sweden, for example) see children learning for fewer hours and for fewer weeks of the years, but achieve far higher standards academically and are much happier children.
Do you really want your children to take part in more learning? Do you feel that the quantity of content of the curriculum isn't sufficient? Do you imagine they will be happier, more well-adjusted, better education humans with more time in school learning long multiplication?
As an ex-primary school teacher, I know very well that the children are exhausted with what they already receive in terms of educational hours. I personally think that they should have more holidays. And I say that as a parent who now works in the private sector and suffers the same struggles as many of you when it comes to desperately scrabbling for childcare during the holidays.
None of the above invalidate the struggles the OP and many of you experience. We should be campaigning for more and more flexible annual leave from our employers. We should be campaigning for more and more affordable/subsidised holiday care options.
Think of what you're asking to take away from your children in asking for more time in school. Our kids deserve time to be kids. The UK's factory style education system is not fit for purpose as it is and I certainly don't want more of it for my child, no matter how convenient the prospect may be for my working hours.