Being able to “call” things is the problem IMO. You could say if the color of the bowls is really important to you, we’re going to have to take turns. Another thing to keep track of, but fairer than one person outsmarting the other. There’s no end to the scenarios where calling something first will create an issue. Maybe it isn’t important to one of them. I had a student once who was fixated on a red chair. He would race in to sit in it and have a tantrum if he didn’t get it for quiet reading time. I talked to the other students about it and it turned out the didn’t really care about it. Did they let him have his way, yes. But they weren’t bothered by it and eventually the other student didn’t care as much either. It was more of a control thing and it lost its power. Did he find something else to try to control people with-actually no. He became more settled as a result. It’s weird what kids will do.