I begin with what is and isn't a dinosaur. Not all reptiles that lived in the Mesozoic Age are dinosaurs. Dinosaurs did not have flippers and live their entire life in the water. Dinosaurs could swim however. Elasmosaurs and others were not dinos. Dinosaurs could not just fly with wings. Pterosaurs weren't dinos. Some of the later dinos had feathers and could glide or fly but could also fly. Dinosaurs had legs that came down straight not bent like those of a crocodile today. I had toy models so the children could chose who was and was not a dinosaur. You could do this with pictures too.
We then played "Name That Dinosaur". I had toy models and placed one in the child's hands, but there hands were behind their back and they guessed which it was by feeling for horns, spikes and claws. The kids love playing and when we were done we sorted them by herbivores and carnivores. Al herbivore dinosaurs walked on 4 legs. Not all dinosaurs that walked on 2 legs were carnivores. You must look at their head and teeth to decide. We then sorted them by the time period they lived in. The Triassic was first and we saw a Plateosaurus. The Jurassic was the time of the large herbivores. The Cretaceous had the largest meat eaters.
We then looked at my Iguana, Ozzy and talked about his difference and similarities to a dinosaur. His legs are bent which make him not a dino. His spines on the back are similar, his tail can whip like a sauropods tail. He's covered in spines.