As someone who works in the field of usability, one of the first things we remind ourselves of in any project is that we don't represent every person in the universe - that there are vast differences between people.
Personally, no. I don't believe I could be the mom who would forget her child. Can I understand how it can happen - possibly. Imagine something out of the routine (I'm making this up, since I don't know anything about the case you're referring to) she forgot to drop the child off at daycare because he was so quiet. She was worried about the fact that her husband had just lost his job and distracted by the fact that she'd just gotten a notice about a registered letter and was worried about a lawsuit against her... So she drove on to work, got out of the car, didn't worry about her child (because she's used to him being in daycare) and went on with her day. It doesn't mean the mother didn't love or care about her child.
You are right that forgetting a child in a car is horrible and inexcusable.
Rachel