Conor,
This Hot and Cold activity from ESERO was originally planned for the youngest classes, with a 1st class you could use it as a prompt and then the children could take the next step by considering if other factors affect the speed with which an ice cube melts.
This could be connected to the concept of temperature, which appears in Science for 1st/2nd class.
• learn that temperature is a measurement of how hot something is
• measure and compare temperatures in different places in the classroom, school and environment.