The shell of each hatching egg is made from calcium carbonate which when submerged in water will dissolve allowing the creature inside to escape and grow. The hatching egg comes inside a clear plastic egg which you fill up with water by removing the screw top this can then be replaced making it water tight. Each hatching egg is ce marked and is not recommended for children under 3 years due to small parts. The ce warning is written in both english spanish and french.