Why were kids allowed to act in the movie Caligula (1979)? To me it seems that the movie is a purely adult movie with sexual activity through the movie. Also, there's a scene where a topless woman was hold kids. How was this allowed?
Caligula is pure trash. It was intended to be an arthouse movie, and Bob Guccione wanted to make it a Penthouse movie. His disagreements with writer Gore Vidal were so preposterous that Vidal eventually disassociated himself with the movie. The only positive of that whole movie was an early appearance by Helen Mirren. She's smoking hot in that movie, and does nude scenes.
As for why children were allowed in it; they were allowed in certain scenes. They were not involved in anything sexual, and a naked body alone is not considered sexual. I don't recall any of the children being naked, but there seems to be a ceiling for a child's age. Remember all the diaper commercials which show children's bare bottoms?