Genius

Addi: Hey, Levi is playing with my hair-doll.
Levi: I had it first.
Addi: Give it to me.
Levi: No!
Addi: Daddy, Levi has my toy! (LOUD)
Me: Ugh
Addi: I know what I can do!

Addi runs to Levi's room. Comes back with his Batman cape.

Addi: Look what I'm playing with, Levi.
Levi: Hey, I want that. Here's this.

Problem solved.