Neither. They burrow into the childs chest and lay their eggs.
Most animals that hunt down prey and est them would start with the limbs so the prey cannot escape. So it would be arms or legs first, but most preditors would tear off the limbs.
If a pack animal, they alpha would start with the chest, often seeking out the heart and liver for the superior nutrients, then the rest of the pack would tear it apart.
However, most insect preditors seek to reproduce, so the wrapping up of prey in webs and injecting the mummified baby with eggs that eat their way out of the torso is the most likely outcome.
Now what you are thinking of is a snake. Snakes start with the head. The limbs fold down for most creatures, making it easier to swallow, as well as once you cut off air, they stop struggling.
Nightmare creatures that enjoy terror would start with the feet so the prey can struggle more. But that's only for fun, not for feeding. An animal would want to be practical.
