This is a cool activity to do with the kids anytime.
You would need to use one of my favourite supplies: Liquid Watercolour Paints.
All you need;
Watercolour Paints (6 colours are used here, but any number is fine)
A Tray For Paints
A Selection of paint brushes.
Start the activity by placing a paper towel onto a tray.
Then let the kids have fun as they touch their brushes to the paper to let the liquid paint soak in. They can also use their fingers to flick and make splatters of paint onto their paper towels. You can encourage them to keep going until the whole paper towel is covered with paint.
The results will be beautiful!