Water beads is fun. We recommend that you only play with it when the children no longer put anything uncontrollably in their mouth. The balls are made of polymers, also known as superabsorbents . This is actually what is in baby diapers and absorbs moisture - often in a smaller granule form and combined with additional layers. They are said to be biodegradable and harmless, but I would still make sure that no one eats them.
And something else about the sustainability of the water pearls Waterbeads nz
Superabsorbents are biodegradable and not plastic waste. We used it for about 5 months. Yes, we threw them away. But there is a better solution: you can "bury" them in a larger flowerpot with a decent goodbye. According to this link here you can mix them with normal flower potting so that we loosen up the existing soil and continue to function as a water reservoir.
Get your water beads in New Zealand at: waterbeads.co.nz