I've just come back from holiday with my family that all went well except for a daily debate about what the time the kids should get up!
We've always known my DC get up much earlier than DN's so I equipped mine with a clock, torch, books, toys etc & told them to stay quietly in their room til 8am knowing it could be nearer to their usual get up time of 7:30. On the first day they slept until 7:50 & when everyone else surfaced SIL kept commenting that my nephew would be really grumpy without his sleep and it was far too early to start the day on your holidays. I agree that 7:30 can't be classed a lie-in but really can't imagine many young children are tucked up asleep past 8am & expecting my DC to creep around until 9am is every bit as 'selfish' as mine are for being up & about before 8.
Maybe I was being overly sensitive but I really felt she was suggesting we were to blame for allowing them up at such an ungodly hour and if we just laid down the law they'd sleep in like her DC. So as not to be accused of drip feeding, we would take them downstairs & shut the kitchen door and wouldn't allow the usual noise but my DC are very much up & raring to go in the morning & definitely not the silent types 
AIBU waking her kids up at this time or is she being unreasonable in expecting to sleep in?
LCN
Ps kids are 2, 3, 6, 6 & 7