My initial thought, in having worked with children and adults with developmental disabilities, was that either a) mom also has a developmental disability or b) has a disorder (maybe anxiety?) that affected her decision making.
Could a parent have done better? Yes, absolutely. I think this is still a societal failure, especially if my hunch is correct.
Edit: Just read the article in full. Mom lost husband in 2020 and was left looking after 4 children with no income. That could be enough to make someone have trouble with more than just day-to-day survival.