Headlight for a Tricycle
This is a headlight I built for my son's tricycle.  It is designed to fit a fisher-price plastic tricycle, but you can tweak the designs (in openSCAD) to mount it on any kind of tricycle you like.  It is perfect for riding in the dark, and my son absolutely loves it.

If you want a cost-effective way to put a light on your own kid's tricycle, you should probably just duct tape a flashlight to the steering wheel and be done with it.  On the other hand, if y...