The children want to paint outside? Then take a bowl with water and a brush and you can get started. This is also a nice alternative if you don't have chalk at hand! You can even paint without a brush.
Find a smooth surface e.g. terrace slabs, walkway slabs, smooth paving stones, garden table or similar.
Attention: You should choose an underground on which you can see the wet well!
Then it can start. Paint what you want and show your works of art quickly! Possibly take a photo before the works of art are dried!
Here are some ideas...
Have fun painting!
The nice thing about this action is: no leaf blows from it, no pens curl from the table or wander into the mouth? You don't have to clean up much (the sun does that).
The most beautiful thing about it is that the children are busy and have fun!