From
http://wdwent.com/
The American Idol Experience
25-minute shows
12:30, 1:30, 4:00, 5:00, 6:00 & 7:00pm
The last show is the finale with the winners of the previous shows of the day. You can exit the theatre but I wouldn't recommend it - it's not like the Epcot entertainment where you can walk up, sample, and leave if you want. The Idol Experience is in an indoor theatre and you vote for the contestant you think is the best. It is like the original version of the show (a Randy Jackson, a Paula Abdul, and a Simon Cowell plus a very energetic host).
I'd recommend it for your kids since they like singers. And now you have the times for it so you can schedule at least one time. It's not a must-see for us but if we are there and it's seating, we go.