Put a cap of food colouring, a splash of coconut essence and some water in the water squirter. Use several squirters in different colours for extra fun.
Lay some old boxes on the grass.
Try to lay the boxes so there are some dimensions to explore. Places for paint to run, places to squirt through or under. If two or more children are playing, set up the boxes so there are opportunities to skirmish.
Hand the children the squirters and move out of the line of fire. Ask them about what the paint is doing on the boxes, what they can see, what they can smell.
If your kids have enjoyed this, why not do messy paint spraying and create some unique works of art.