We bump bellies.
We paint bellies.
We read books about babies in bellies.
And just when we aren't sure he "gets it", he shows us......
When perusing the stuffed animals in a store, he picks out two and heads toward the door.
I call to him, "You can only take one".
And so he turns to his auntie and says, "Put belly... in belly"... As in, that's where Mommy's carrying a baby, so you can carry this for me:)