These are ammunition (projectiles) for compatible toys called orbeez guns or gel blasters. These gel balls are generally called orbeez or gellets on the websites. They have a specific, standard diameter for use as ammunition for these toys. They come in several colours and are offered by a range of different brands. They are generally sold dehydrated and need to be immersed in water for several hours so that they can soak up the water before being used. They are also available in larger diameters, for uses ranging from decoration to controlled watering of plants. These beads are reputed to be 100% biodegradable and non-toxic, but this information was gleaned from the internet, so there's no guarantee.