Water beads are so fun! You can find them at the dollar store, Michael’s, and even online. They are meant to go in vases with flowers and come in all kinds of colors. They are also cheap ($1-2) and easy to replace.
Kids love to play with these, they especially love to run their hands through them (a great sensory game). I first learned about these in Graduate school to use in therapy with children as a sensory reward. You can make up games or hide things in them. I’ve had kids play for over an hour just running their hands through the beads.
The drawback is that with younger kids you have to make sure that they do not put them in their mouth. They are not toxic, however they look fun to eat and can be quite a temptation!