Most of the 3d prints prints we did feels like just-for-fun, without much practical use. But it was fun for the kids, it did help to improve their computer skills. I think personalized bookmarks, key chains, nametags, are somethings that are actually useful.
TinkerCad and Ultimake Cura softwares were used (both are free). TinkerCad is a free website for designing, no need to download. Ultimaker Cura needs to be downloaded, it converts the 3D model into printable format, it also shows the time and amount of material required.
We printed from the Library (there is a charge).