There is so much energy running through those kids at the tournaments that they do a better job of being up and energetic all night than the parents do (believe Chris has pictures to back that up).
The all nighters are great for team bonding. The girls get to know each other a lot more during the course of time they are off the field. I saw coaches yawn last year during the tournaments, but never saw a player yawn or look unattentive.
Now, the day after on the other hand.....