I love the book I'm Not Just a Scribble by Diane Alber for many reasons. First, the story and images are cute, simple and clever. It will appeal to your two year old as much as your four year old. Secondly, it's a story about inclusion, resilience and acceptance, ideas that all children will eventually have to deal with. And thirdly, you can immediately get your kids doing "Scribble Art" after reading this book. The scribble art process is a gentle way to introduce your children to the world of representational art.
All you will need to get started are a copy of the book, some paper and a box of markers. The book comes with stickers for eyes and mouths.
I read the book to my kids, then showed them the stickers and asked them if they wanted to make scribble people. They both enthusiastically said, "Yes!" My 4 year old didn't need any instructions, but my two year old did. I did a quick scribble, showed him how to place stickers on the face and how to draw the arms and legs. I should mention that this kid does not know how to draw stick figures yet, so I was impressed when he was able to place arm and leg lines in fairly accurate positions.
This process will give your child the tools and confidence to create figures even if they have never created a representational work of art before! It will also get their imaginations going! My 4 year old made more than ten scribble people on that first night. Since then she has gone back to our art corner and made more scribble people on her own. There are flying scribbles, scribbles in cars, fireman scribbles, Mommy, Daddy and Baby scribble people and the list goes on!
I could also see this being a great project for talking about emotions. If you don't have the book or you run out of stickers you could make your own by drawing a bunch of eyes and mouths on white paper and cutting them out. You could make angry eyes, sad eyes, tired eyes, etc. If your child is older, they could draw the eyes and mouths themselves. If you want to buy more eyes/mouths you can do that here. Have fun scribbling!