Well my 12 yo couldn't be left on her own all summer. She does have SEN but in theory could go to the park on her own. Only she is very anxious and she would hate it.
She has 9 weeks off this year (state school). DH is off for 2 weeks, we have 1 week all off when we will go away, 1 week already booked at PGL, 2 weeks already booked at Kings Camps, still have 3 weeks to cover. I can only take a week off in the summer because I have to cover Xmas (3 weeks) and 1 of the Easter weeks.
We are very lucky here that there are several different providers; a couple of national chains, the local Uni, a couple of private companies, and all of them take vouchers. There are more specialist things available but they don't take vouchers and cost a fortune.
As a 12 yo back in the 70s I'm sure I didn't get looked after, except that my DM only worked during term time so would have been home. I can remember feeling quite surprised that a school-friend was taken everywhere by car when I normally went to town on a Saturday on the bus on my own. BUT it was a different time.
There wasn't anywhere near the traffic that there is now, and as a pp mentioned, people looked out for you. I've said before, if I did anything wrong in public my DM would know about it before I got back. Mrs Bloggs from up the road would have been straight round to tell tales on me. People felt they had the right to step in and interfere, whereas now they don't. I'm not confident that people would look out for my DD in the same way.