Imagine a battery-powered device the size of a lip-balm. It contains a mini electric motor with a rotating brush. Before use, you squirt in some non-toxic sterilizing gel.
After digging in the dirt, your child inserts one finger at a time, for a few seconds each. A fun experience results in clean and sterilized fingers. Your child is protected from infecting themselves with all sorts of germs. This is especially useful if your child has a habit of biting their nails, sucking on their fingers, etc.
The device is water-tight, can be washed and the battery charged via induction. You place it on any existing electric toothbrush charger.
Since the device is for kids, it should be in vivid colors (unlike the header image) and have some blinking diodes while in operation.
The manufacturing could be crowd-funded via Kickstarter or a similar platform.