I'm still very new at this so it's not as elegant as some of the other designs out there, but I noted a severe lack of Harry Potter themed fidgets (and the one I found was a bit large even for adult hands) so I'm making a few to share. I'm a Chapter Organizer of a community-based Harry Potter Alliance chapter and would be happy to see these getting spread throughout the HPA. Don't make them to sell for profit, but I'm OK with the design being used for fundraising purposes for HPA groups or other educational non-profits.
Designed in TinkerCAD, printed on a New Matter MOD-t (I think I used the fast pre-sets in the white one in the photo).
For others who want to make fidget spinners, I've found the best opening size for the bearing is 22.55mm - anything smaller requires a hammer to get the bearing in, anything bigger the bearing falls out. At that size, it can be pushed in with thumbs & seated into the plastic well by pressing on a table and is removable with effort but not likely to pop out.
My designs for spinners are not weighted after my husband lost control of one he made with nuts in the arms and nearly whacked our baby in the head with it. If you want to take this design and put in some ball bearings in the wings, go ahead and do it yourself. Don't ask me to do it, Mama says no.
New Matter MOD-t
If you want to use more plastic & do more infill, the additional weight will likely help improve spin.