Pickoff Moves to 3rd

Question
OK, my son is 10 years old and they play regular baseball rules with stealing and all.  My son was pitching and he had a kid on 3rd base.  He faked a pickoff move by picking up his left leg (He is a right hander) and stepping straight at 3rd without throwing.  Is this considered a balk?  For some reason, I thought it wasn't?  I could have sworn that I've seen pitchers fake the pickoff to 3rd and then turn around and throw or fake to 1st base on a pickoff.  Is that OK?  Thanks for your help!

Answer
His foot has to come off the mound, so he can pick up his leg and fake the throw but his back leg has to come off the mound in some way. When you see guys faking to third and throwing to first, they're allowed to because when they go to turn to first the back foot automatically comes off