How old are the kids?

S'pore being a duty-free port has some fine shopping centers. Steer clear of the Orchard Towers mall after dark though.

I second the Zoo and the botanical gardens recommendations.

I went to high school in S'pore. I'm not sure where you're from but one of my favorite activities was visiting the stalls. Great atmosphere, something you'll never experience in the states. Oh, and the food? To die for! Sentosa is a tourist trap. I lived in S'pore for three years and never went to Sentosa, can you believe it?

Have fun.