Best way to train a 3v3 carousel with 12 players?

Four teams of three on two pitches is exactly how I’d start with 12. I’d probably keep the teams together for the first couple of games. It gives them a chance to work something out with the same two teammates instead of meeting a completely new problem every six minutes. Then I’d mix them later if the games are one-sided, if certain players are dominating, or simply because you want them playing with different people. Keep the changeover really simple. Game finishes, teams know which pitch they are moving to, spare balls are ready and the next one starts. The danger with a carousel is that the adults spend longer organising the rotation than the children spend playing. If you need a diagram to remember who goes where, simplify it.