I have put an 11 year old in the trundle at POR, he didn't complain. Disney had no problems with putting him in that bed.
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And you had three adults? I thought the thread where this was on (prob a year ago now), they were told with three adults, and those ages kids, you couldn't have 5 with a trundle. I guess it pays to keep asking. At that time, I thought the poster of that thread was told age 9.