3 is a great age for it. We had over looked this the last few trips and finally decided to do it on our 2015 trip. Our 7 and 12 yr old boys (at the time) loved it and both had parts!
Could you say more about what is expected of the children? Are they given lines? Actions? Do the silverware-type background characters just have to stand there? I have an 8yo son who wants to go in his Beast-at-the-ball costume in hopes of getting to be the Beast, a shy 6yo son who will still probably want to be involved in the background only, and 2.5yo daughter who will want to follow them up to the front and do...something.