One of the things I accomplished this past weekend was painting these seashells for my daughter.
I had bought a basket of shells and underneath all the pretty ones were the ugly ones. I added two coats of paint and a layer of mod podge and made them into a fun and pretty new learning toy. She already knows most of her colors, but I made two of each color so she could learn about matching. I also made one bigger than the other to teach her about size.
I will ask her to match the colors and then ask her which one is BIGGER or smaller. It really keeps her occupied. I do not leave her alone with these though, and would not recommend small children play with this type of thing alone. I used all non-toxic materials, but shells can be sharp.
So if you make some for your little one, make sure someone is with them when they have them.