When my son was three I found out about these things called water beads or crystal soil which are designed to be put in vases around plants, presumably for decorative purposes, although I would not personally do that.
Anyway, apparently everyone with kids knows about them because they are non-toxic, bio-degradable and make for great ‘sensory’ play (for those who are old enough not to eat them). Here is our experience with them.
I ordered an inexpensive little package of Crystal Soil from Amazon, but I think you can get them at craft stores and dollar stores too. They are tiny bead shaped things that you soak in water for a few hours, after which they absorb much of the water and grow to be squishy marble-sized balls.
Here’s the package I have, and here were the somewhat unclear instructions on it (below), but the general process seemed pretty self explanatory for my purposes.
1. add water 400G on the product. about 4 hours it will grow up.
2. one clear beauty satiety face will grow up.
3. when the flower want to oxygen and nutrition, I will help you too much. [sic]
Obviously something lost in translation there.
Prepare to have to wait about 3-4 hours (soak early in the morning or even at night to use the next day) before the kiddos can get at ’em, so they have plenty of time to absorb water.
Here’s how they look after they begin to grow (we did two different batches of color for these pictures):
My son loves these. They are slippery, bouncy and colorful. Before when we used them, he played with them in a big plastic tub at the kitchen table. This time, we added them to his water table outside. You don’t have to dump them in water, but I would recommend a large container and maybe going outside with them because they tend to end up everywhere, and they will eventually crumble into little gelatinous gobs, (which can be hard to dig out if they roll under the refrigerator).
If they dry out, they eventually shrink a bit, but if your child does not squeeze them, they will last for days.
My son eventually dumped them down his slide and into the grass and pushed them through the cracks in our deck after playing with them (for nearly two hours!), but they eventually dry up and dissolve away.
I found this project idea Here.
*Please remember to closely supervise small children (or pets) around these, so they don’t put them in their mouths!