My experiment with 3D printing some childproofing. Only install if you trust your 3d printer and your skills as much a major manufacturer.
I'm pretty confident that if my son can break this open, we need to lock the doors.
They are designed to require a certain hand size to reach both sides of the cover and pinch through to turn the knob.
I designed this to fit around 5 different door knobs on my house, so it will probably fit yours. The design is print–in–place moving part with with no need for support.
A small zip tie through the included channel secures the cover.
Update: v25 adds missing fillet. Oops!
Extra perimeters and a higher infill will make this a lot stronger. That's good for a safety device.
I am not liable for your printing choices. There is no way to certify your print and this device will be safe at all.
Designer from Internet