Have a go at making your own Magic Rainbow Milk. Kids of all ages will love it! Magic Rainbow Milk is cheap, quick and easy to set up and if you do it outside (highly recommended!), theres not too much mess to clean up afterwards.
Have a go at making your own rainbow salt tray. Toddlers and preschoolers will have lots of fun watching the colours come through when they draw pictures, create patterns and write their name in the salt. It is cheap to set up and you will already have the items at home.