In our house, the answer to this question is six years old. And so, here is a hat that does meet with the approval of our biggest girl.
This new hat coincides with her losing her first tooth. Wow. So grown up. And, unwilling to contemplate animal ears on hats (even if she has given a few admiring inspections of her little sister's new bunny rabbit hat).
Anyhow, this hat is just a smaller version of the bobble hat I made for myself. I cast on 36 stitches instead of 41, and then made the finished length of the hat a bit smaller, too, before following the same instructions of shaping the crown. It worked, and the hat fits. The biggest girl was not too impressed at the plain black hat I presented her with, until I explained I was planning to teach her how to make a red pom pom, so that she could make it look like Minnie the Minx. That went down very well.
What's the going rate for the tooth fairy to leave for a tooth, we wondered. The consensus came back with £1. But maybe a bit less for subsequent ones - depending on how much change the tooth fairy has in her purse...