I believe my son was 6 or 7, when I took him on it. He loved it, even the studio tour. However, by the end of the 6 days, he was exhausted. You have to get up early almost every day, and stay up late too. So I would probably recommend the 4 day. The guides do their best to keep the kids engaged.
it really depends on the kid of course.
I don’t think the 4 day was available when we did it, about 6 years ago.