Toddlers May Learn Language By Data Mining
I've also read, though, that children quite often use verb forms that adults just don't - e.g. "runned"; and that this often comes after they've used "run" correctly - and the theory that I read was that children start to work out that to create the past tense you put "ed" on the end. Which, as we know, generally works. It's just they haven't worked out when it doesn't.
I'm not sure if that's all children, or just some of them. I've not got any, but do have a lot of nephews / nieces - and it seems that some do use "runned" and some don't seem to.