Two growing acrobats maybe?

I have two full-blown growing acrobats inside me.

One flips, the other flops.

One tosses, the other turns.

One's upside down, the other is right side up.

I'm ready for bed, they're ready to swing.

I'm trying to sleep, they're breakdancing.

I'm sound asleep, they wake me playing the drums.

I'm in a meeting, they make me laugh by kicking at my belly button (so very ticklish there).

This is pretty nifty. There is life inside me.

Life can only get more interesting.