C.B.
I love theme gifts and your idea is great. You could add some sand toys or wrap everything in a sand bucket with cellophane around it.
Other ideas might be books (bedtime theme?) or bath toys and a cute hooded towel.
I had a friend who wisely suggested you buy toys for an older age, like 18 mos or 24 mos since we all know they will be old enough before we know it. The parents can store them until the child is ready.
Enjoy the party!