Toes are important, especially when you are 3. They need to be checked on often, and counted, and made sure that they are all there. Often.
And, sometimes when you are three, you want to control your brother in the session, who is smaller, but yells just as loud.
Parents always freak out when kids act like kids. Please don't freak. I have two kids, I teach kids, I photograph kids, I know kids can be jerks to each other, and sometimes it even makes cute photos, and I will laugh, because I have 4 siblings. I know how to beat them up with the best of 'em. Let the kids be silly. Let the kids be kids, and I will capture both sides!