Try taking your children outdoors to paint and see what they come up with. Children who are out in the garden all day experience continuous change. Temperature and light fluctuate from hour to hour, scents and sounds vary from one season to the next and there is a progression of flowers and seeds, insects and birds over time. These nuances build children's subconscious knowledge and love of the world they live in, and inspire creativity.
So bring art, wet play and mealtimes into the garden whenever possible. You will find that children respond quite differently to these activities when they take place outdoors.