There’s a screenshot in Mr Menno’s twitter thread which mentions a workshop in the Play Studio between 2pm and 4pm which “explores protest, sound and dress up”. It looks like the people leading the kids workshop then took the workshop participants on a protest march or parade through the galleries (you can see the kids are holding long tubes which are some kind of homemade percussion instrument) and ended up in the gallery with the discussion panel taking place at 4pm and which was age 16+. That panel discussion was not the event with the person in their underwear.
In his twitter thread Mr Menno says that the Oestro Generation pop up (which was the event with the poetry reading in underwear) was elsewhere in the museum.
People seem to be assuming that the children were taken into the gallery with the semi-dressed person. But that isn’t what Mr Menno says in his twitter post.
As you say we don’t know what the publicity material for the workshop said, other than that screenshot.