A tried and tested classic! Painting with potato stamps is lots of fun and cheap and easy to do at home. Toddlers and preschoolers will love getting their hands messy and creating some great pieces of art.
Try stepping back when your kids complain about feeling bored. This will empower them to think for themselves and learn to be resilient. It will also encourage them to find their own way out of the boredom, and the problem-solving process helps them feel good about themselves.