The reports from the hostages themselves said the hostages removed their own clothes because where they were being held was ubearably hot, and they were allowed little, and later no, water.
I don't think kids would strip all their clothes just for it being hot --- when it's over 100 plus in a room, you are not cooler by being naked and these kids were too terrified to make a move on their own. Even middle school and elementary school kids feel more vulnerable without clothes, no way do I believe they removed their own clothes for innocent reasons.