Great point, and ya that is a tough one. I will have to think on this but obviously the initial answer is no. I hate more regulation but I think protecting kids from enterprising parents is important.
Even if you accept that idea, 18 is a bit much. A 14 year old for example can meaningfully consent to being an actor in a movie I think.
I mean, I never got why this is supposedly the one situation where child labor is seen as acceptable in the first place.