Prehistoric gastropods (mollusks) and coral fossils are EVERYWHERE if you live in a prehistoric sea! We found these on a nature walk in a local forest preserve, for instance.
Google what your locality looked like back in the day, and then start looking down. I see one almost every time I am on a walk... And can even find them in landscaping rocks!
Here are some fantastic resources for adults, as well the American Museum of Natural History's section entirely devoted to introducing and supporting your kids' interest in paleontology.