You get an actress who's late teens/early 20s and she can be believable as a 17 year old for several seasons. But an actress playing an 11 year old will only be believable for one. It works for a movie or a miniseries, but not for something you plan on working long term...
It sucks, but it is what it is. I was a fan of Everything Sucks! on Netflix. They did one season that ended with a cliffhanger and then it was canceled after that. I was hoping someone would bring it back, but considering they used a lot of young teen actors to play the roles, it wouldn't work even if they did.