DCs are 11 and 13 (yr7 and yr9). We've left them for two-three hrs in the daytime or early evening before 8.30.
But now friends who's oldest DC are the same age as mine have started to leave them to go out (locally) so maybe till 11-11.30 ish. Some also have younger siblings, 7-8yrs, too.
When my DCs are home alone they just stay in their own rooms playing on their gaming devices, quite happy.
Part of me thinks it'd be fine for us to pop to the local, I know I was babysitting when I was in year 9.
But then part of me thinks they're a bit too young. I just don't know!
What do other people do?