How would that help them make money, retaining users is what it's all about, finding links with people years after college is great. I doubt Facebook just wants to connect you when your in school, they want to map out your whole life, that friend time line is really cool.
As was pointed out, the ideas were about protecting the children rather than making money.
But, they could make money using an adult oriented site that didn't permit children. Then, have the children's only access be through something like the school based system I proposed. Then, kids are talking to kids, and adults are talking to adults.