Every child is different.
The son and heir never went to bed before about 9:30/10:00 at the very earliest, much to the horror of his grandparents.
He never had any trouble getting up for school about 7:30.
We gave up putting him to bed any earlier as he did not go to sleep and it seemed cruel to condemn him to hours of dark boredom.
He is in his late twenties now and still doesn't sleep much.
If they are not sleepy I'd guess they're getting enough.