This is your warning, go and freeze loads of water now. Ice play is fantastic for children's play and exploration in so many ways.
To build your ice castle you simply need a mountain of ice cubes. A variety of shapes and sizes work perfectly as they learn how to make their structure stronger and what shapes work the best. As the ice melts you can discuss why this might be happening and what may happen to their castle in a given period of time.
Time yourselves to see what you can build it before it all melts.