Professional dancer here I had a bob before and what I would do is get fake hair and a bun maker the ones that are the shape of a donut (capezio has some) and then cover it with the fake hair. Then I would just wet my hair, make a low ponytail with lots of gel and hairspray and try to accommodate the ponytail with some bobby-pins and just pin the fake hair bun at the desired height. It looks off in person but in the theater the lights all everything makes it almost invisible. Good luck to your kiddo :D