Changi is a great airport and there is plenty to do. There is even a swimming pool to use (though I don't know whether it is open at night.) Singapore is easy to get around - the public transport system is great is you feel brave enough to head out for a couple of hours with the kiddies. (I didn't have any problems as a transit passenger leaving the terminal but I guess you could double check with a travel agent). I think there is a playground in every
terminal.