I appreciate everyone's insightful comments here. I really enjoy coming on a soccer forum and finding a thread that discusses soccer issues.
In this instance, I think it really depends on what your endgame is. If it is to play in college, then yes, you need as much playing time as possible. You get better by being on the field and you get more exposure being on the field. If your child doesn't have those aspirations, I think two keepers and split playing time can be a good thing. Other than the top 1%, kids play sports to have some fun, get some exercise, and learn life lessons. There are a lot of life lessons that can be learned by competing with another keeper: Hard work to earn playing time. Learning to get along with and be friends with someone who you are competing with. Rooting for your competition to do well because it is best for the team, although it may hurt you personally. And so many more....
My keeper is 12 and hasn't hit a growth spirt yet, so I'm not sure if there is college soccer in the future or not. But, if some of the lessons above can be learned early through having two keepers, it's a win.