I think Baby Wario will be able to place bob-ombs on the ground in addition to collecting coins with his giant magnet. However, the bomb will explode about 1.7 seconds after lighting it, so you'd have to run like the wind away from the Bob-omb to avoid dying in the explosion.
Baby Bowser would, obivously, be able to shoot Fireballs from mouth. Maybe he could also power up your ground pound so it caused vibrations in the ground. But that would be a bit too powerful, so maybe not.
I don't know what Wi-Fi play would be like, though. Co-op, maybe?