It's likely that most dinosaurs also used a mound of vegetation or sand to help insulate the eggs. It's unlikely they used their bodies like most birds do. The shell of dinosaur eggs contains large pores to supply the embryo with oxygen, very similar to crocodile eggs. Guarding the eggs greatly enhances their survival against predators. Such behaviour in dinosaurs would not have been unusual.
Sound plays an important role during hatching as it triggers maternal behaviour in adult crocodiles.
It probably did the same in dinosaurs. Soft calls from within the eggs alert the female crocodile that her nest is due to hatch. She breaks open the hardened outer layers using her front legs and jaws - the hatchlings might never break free otherwise. Further calling encourages the female to carefully pick hatchlings up in her jaws. This inhibits the swallowing reflex as she carries them to the relative safety of the water.