I bought this "Grow Your Own Crystal" kit at Micheal's. It came with three small packets of crystals (Purple, Blue and Clear). They are just like large water beads that are not round.
Like water beads, you just submerge the crystals in water and wait for them to grow.
My daughter pulled out her binoculars to help her watch the crystals grow. They take a while to reach their full size so she went back to playing and checked back about every ten minutes.
She really liked these because they are different then the small water beads she usually plays with. She called them squishy diamonds and pretended she had found a treasure.
After playing with them for a while she asked for a towel to put her diamonds on and then pulled out her magnifying glass. She spent a few minutes in deep concentration inspecting her diamonds.
We played with these for a couple times by themselves and then she decided to mix them with her water beads. She has been having fun with the squishy mix of beads and "diamonds".