This cloud has an internal space to embed a magnet while printing. It's a great practical decoration, and the magnet won't ever fall out.
Design features
The model is 50 mm wide, which should pass the small parts test for children under 3 years old (please supervise your children and use your judgment at all times).
The magnet is fully embedded and can't be removed (safer than a glued-on magnet).
Chamfered and rounded edges for easy handling.
When printing in flex filament it will hurt less when thrown.
I've rendered it for a 15x5mm and a 15x10mm magnet. The 15x10 will easily hold cardstock up by the drywall screws, and will also makes a good stud finder.
Message me if you'd like a different size.
Printing instructions
I recommend flex with 10% infill.
Slice the .stl file to include a pause after the magnet cavity (around 11.4 mm, depending on your layer height and which magnet size you're using).
Insert the magnet during the pause (glue isn't necessary for flex material, but if you're using something hard it will prevent rattles). Check that the magnet orientation is suitable for your use.
Note: The .gcode file I've included has a custom pause algorithm. Upon resume it will extrude a bit and begin a 4 second move to give you time to wipe excess material.
Safety notes
Magnets can be dangerous.
Please supervise your children at all times.
Notes
I designed this model in OpenSCAD and it's fully parameterized. If you'd like a simple modification (i.e., magnet size, height, etc.), send me a message and I'll see what I can do.