Too broad a topic tbh.
I dont let smallest boy LT sleep in at weekends for example and in general did the same with the girls as i see that as a waste of the day. Too much to do in life for lying in till 12. That said oldest girl LT will sleep in till 12 but that is because she got in hammered at 4
Smallest boy LT who is now 12 goes up at 10 now and has always had a set time as did the girls. Kids need a structure and so do parents for down time etc