When the work is a net negative to the child. Light farm work can be fun and healthy for a child and beneficial to the family. Just don't make the 8y/o chuck bales of hay. Keep him in the garden pulling weeds and harvesting peppers, or throwing flakes of hay to the goats and sheep.

Child acting and fame can be psychologically damaging to a child, even if the casting couch issue is solved (by #millstones?).