Pyrrah - you've fallen for the biggest misconception surrounding teaching ever. Do you believe teachers only work for the hours that children are present? Ever single lesson has to be planned for and then assessed afterwards. This cannot occur when children are in school. There are also meetings to be had within schools, with parents and with outside agencies. These cannot take place where children are present.
So whilst the child's school day is 8:50-3:20 or whatever, the teachers working day is not this. The teachers must be in before then, and they will then have work to do afterwards to, this bringing them to what you might call a normal working day. The holidays are not 13 weeks of free time. They are non contact time in many ways - as lessons still need planning. classrooms preparing, work assessing, etc. Every teacher I know has always worked for many of the days in their holidays. Also bear in mind that teachers are not actually paid for those holidays too.
So okay - make school days longer for children - but then pay teachers more to cover this and cover the extra from the holidays - oh, and don't forget you expect a lower quality of lesson plans because they'll be no time left to do that!
Not to mention that the children will end up shattered too - so by 4pm they'll be learning very little anyway. They'll be hungry, tired and grumpy. Some of these children are only 4 and 5 after all.
What about chance for extra curricular, non school based activities too = swimming, drama club, ballet, football, music lessons..... or simply just the chance to relax and play with friends and family.
After all school is not childcare is it? And as for parents needing childcare - well, school has existed in a similar form for years - the idea that parents need to have childcare organised is not a new one. You know that when you chose to begin a family!