However, as far as your actual question is concerned, I can't actually think of a word. Is he actually angry? Is he playing? I don't really see how you can get angry in a childish way, and I don't understand why he would hide his face!
When children get angry, it can sometimes be called petulant. This is when they maybe stamp their foot, stick out their bottom lip and sulk, but it's not necessarily angry, they are just being difficult!
Student or Learner