Why are other circumstances relevant? Rationally speaking, here is a source of energy that you do not need to work for. The easiest decision if one ignores unnecessary social taboos one is brainwashed into.
Well, let's look at just one suggestion from secular philosophy: Kant's "categorical imperative". What he said was that something should be considered "good" or morally acceptable only if one could wish that it become a general rule, applicable to all.
Let's apply that to eating your babies. Suppose that we were to propose a general rule that all mothers should follow: "Every mother should eat her babies, because they are a source of energy you do not need to work for."
What would be the result of this proposed rule? Answer: no more humans, after a relatively short period of time. And so, a rule apparently based on self-interest is shown to be ultimately detrimental to self-interest.
Perhaps you think this rule would be fine in the short term, and we shouldn't worry about the long term. Then, you are proposing another general moral principle "Always think only in the short-term." But now apply Kant's standard to that rule...
See how this works?