The best books about picnics for preschoolers are:
1. The Very Hungry Caterpillar by Eric Carle
2. The Cat in the Hat by Dr. Seuss
3. The Very Busy Spider by Eric Carle
4. The Very Quiet Cricket by Eric Carle
5. The Grouchy Ladybug by Eric Carle
These are all great books that teach children about picnics, insects, and other animals. They are also all very entertaining, so your child will likely enjoy them.