As long as the boys served a purpose to Darlie in some way shape or form in her own mind the boys were treated O.K. Not that she was not detached from them then, she just used them to elevate herself in her own mind.
But when the reality hit, that they were seen as a "burden" and a drain on money, well they no longer "enriched" Darlie she saw them as the problem, the source of misery, of work, of money being spent. Well they were no longer useful to her and she had no problem killing them as they were and always were seen as "objects" to her.
She played the part, but in reality she no did not love those boys from day one. Because Darlie only see the world from Darlie perspective, sees it through her own needs, she is the most important person in the world and no one else matters.
I agree with Cami, Darlie has a profound character defect and disturbance also called Personality Disorders. Her whole life had no substance, it was all superficial, all looks, all appearances that is until real life invaded her fantasy of what her life should be like, what she felt she deserved, and being a stay a home Mom, with three kids, no car, income decreasing, no skills, and losing her looks was not the life that Darlie thought she deserved.