Think of several different activities, they have to either be done quickly (hare) or very slowly (tortoise),

Examples
Hare: hopping, skipping, writing their name, 10 things that start with the letter s, putting pillows into pillowcases.

Tortoise: eating a piece of chocolate, running round the garden, moon walking, pretending to climb a ladder or anything that can be done slowly

Use your imagination sucking ice cream through a straw is always great fun to watch.