little kids

So yesterday I went over to my aunt and uncles to babysit my cousins and spend the night. My aunt told me that they had been up until like 11 last night and the woke up at 5:30, so they should be tired. I let both of them stay up about an hour later then their bed(10) time just to make sure they would go to sleep without making a fuss. Both of them were not tired, and then came upstairs into my room at 7 in the morning!! I thought little kids needed lots of sleep! so why do they wake up so early?!