4 machines, around 20 kids, tournament format?

Hi everyone,

My daughter is having a birthday party on the weekend and I wanted to run a short tournament for them. I have 4 machines and there should be around 20 teenagers there. What would be the best format?

Thanks.

Thanks for the response. Sorry I've never played in a tournament before, could you briefly explain what those terms mean?

We ended up just letting them play for a couple of hours. They were all pretty new to pinball so it turned out that a tournament wasn't really necessary. Thanks for the replies though.