A little better all the time

Before I get to the story, I have to give you a little background. Child A has been with us a few months and is usually resistant to cleaning up.  He also likes to throw tantrums and hit when he's upset. He's been getting a little better all the time and has started to follow directions the first time we ask.
Today, child B was coloring and got upset, throwing our box of colored pencils down.  I asked him to clean up, using every strategy in my toolbox, but he was too upset to listen. I was just about to take him to the calm-down area when I heard Child A say, "B, will you play with me?"
I told him, "I'm sorry, A, but B needs to clean up first. When he's done, he can play with you."
Then Child A came over, picked up all of the colored pencils and asked, "Now can he play?"
What else could I say but "Of course!"