With my niece, she does stuff like that, throw her food and sometimes think it's a game. So what I do is take away her food for 2 minutes and then proceed to explain to her it's not nice the throw food and say "are you going to behave?" if she says yes I give her, her food back. (I give it back regardless after the 2 minutes) and sit there with her and watch her eat until she is finished.