how old are your furkids? When Casper and Kitty were younger (oh, they're so old now ,almost 7 months), we had the same thing going on here, they just kept playing like maniacs, night and day. They did sleep a bit though, but mostly they played.
Don't worry, when they're tired enough, they'll sleep and you have a nice and peaceful house (yeah, as if that's possible with cats around ). How many cats you have?