Just got rockband for ps3 and tried to hook it up so my kids could play and the drums and guitar wont play, just the microphone. what is wrong or what else could i do?

Well, there are receivers that must be plugged into the PS3, in order for the machine to detect the guitars or whatever. I’m sure you plugged them in, but I can’t think of anything else.

If everything is plugged in correctly and it still won’t work, I think I remember having to allow the game itself to detect each component that I was using.
For example, once you turn on the game, before preparing to play a song, the game has to know what exactly you are using (drums, one or both guitars, microphone) because you don’t have to use everything to play. That’s the only thing I can think of.