A long answer: when your child gets rated, s/he is ready for any tournaments. The earlier s/he gets some experience of large tournaments, the earlier s/he could cut off the cord of scholastic tournaments. In large tournaments, most likely s/he will play long time-control, and play against some adults. S/he could learn how to play patiently, how to think thoroughly, how to control the tempo of her/his play, and how to plan out end games. S/he will get the experiences and lessons s/he needs when s/he becomes more advanced earlier.
Looking at one player's tournament history, I found that he has played for about 5 years, and about 300 tournaments, but he only stays at 1300. He can't be said not diligent, one tournament every week, but he is not making progress as expected. Why? Looking deeply, there is no large tournaments in history. Most of them are league tournaments, which is one game a week. I believe he is also taking the chess lesson every week at the club. Other than leagues, the others are exclusively scholastic tournaments, local, state, and national. This is not a rare case. In fact, if I see a player stuck in under 1000 for a few years, most likely I will see this "never wean" pattern. It's very sad that they stay in this "baby" status, though they have put in a lot of effort.
Whenever your child reaches 800 level, s/he should consider large tournaments. S/he could start with the lowest section: such as under 1200, preparing to lose all her/his games. The experience s/he gains will benefit her/him forever. With such a low rating, s/he actually has one advantage: not afraid of losing rating. Equipped with this braveness, s/he may outperform her/himself. That's what usually happens.