Seriously? You're asking us what a family could possibly do for 6 hours.

Eat something.
Drink something.
People watch.
Read a book/magazine/newspaper.
Sodoku, crosswords, word search, card games
Video games
Walk around
Bring a ball to play catch with
Play games that families play on road trips (I spy, 20 questions)
Have a conversation
Write in a journal
Take a nap
Explore the airport
Draw a picture

I'm assuming you have to exit and check back in for your next flight? Walk around downstairs where the airport link train service is at. Heck, ride the train around for an hour or two.