IANAL, but the word you are looking for is intent:

https://en.wikipedia.org/wiki/Intention_(criminal_law)

If it's clear the mother went to the woods to create this environment to kill the child, then a state could consider prosecuting.

If there was a plane crash and it was clear that the mother was distraught and this was a side effect of the crash, I don't think most states with prosecute, but again, depends on the state.