Coat hook for kids. Here is Autodesk Inventor files for fixing and customing hooks or background. You can put your kids initial on the hook for example.

I'm kinda noob with this 3d printing thing, but I printed one out with ABS with 0,25 mm layer height, 0,2 infill (rectilinear, 45 deg) and 2 perimeters. You can see the outcome in the picture. I scaled the hook part up 5 % because then it stays put when you press it in it's place and it comes off when you twist and pull it outwards.