I played a level online where it looked like Bowser Jr. threw hammers. I know Bowser does this in the original game.
I tried dragging a Hammer Bros. onto them, but this just replaces them with the Hammer Bros.
How do you make them throw hammers?
Side note: I know putting Bowser Jr. into the Koopa Clown Car makes him throw shells... and putting Bowser into the Koopa Clown Car makes him throw Bob-Ombs.