I have a much simpler solution. I read before my son (5) one to two books, and he is allowed to watch a short movie (Lego technics, marble run, that kind of stuff). Sound is OK, if it is relaxed (so not music with 120 BPM, but lo-fi OK). Then he watches something of about 10 minutes. If he has to go to school tomorrow, he knows that's it, but in vacations and weekends he may watch another one. After he is done, he likes to pick the next movie for tomorrow (very important for him).