Toothbrushes for tiny tots don't always fit in standard toothbrush holders per say. They're either too short, or too far away from the edge of the counter for them to reach. Instead, try using a sponge holder — here's how!
Although it sounds a little wacky to suggest using something so specific for another purpose, by sticking on a suction cup sponge holder to the inside of your bathroom sink (or the outside if you have a pedestal) you've created a perfect spot for little hands to get a hold of their dental hygiene products.
It's bin, with holes in the bottom, makes it an ideal place to store toothbrushes, toothpaste and anything else they might need. Sometimes all you need is the right tool for the job (even if they're usually used in the kitchen!). We found the one pictured above for around $6 on Amazon, though we're pretty sure you could find one locally that would fit your needs!