As howtheduck said, Elly never really embraced her role of mother; she clearly doesn't like her children as human beings because they have wills of their own which clash with her need to focus on her own wants and needs twenty-four hours a day, seven days a week. She also doesn't like doing all the necessary chores that, in her mind, are a horrible imposition that keep her from some grand and glorious destiny she doesn't have the tenacity to work towards. What's more, she doesn't have in it her to console the offsprings when their feelings have been hurt or when they're scared because they cruelly want her to think about someone who isn't her. The end result is that she's destined to end up wanting to own their horses because that's the only way she sees to keep them in her life; she was led to expect that their childhood would be a time of magic, wonder and happiness and it didn't turn out like that; all she got was shouting, embarrassment and disappointment. Where that all falls down is that she doesn't realize (or especially want to) that her default negativity, her refusal to put down the rake and go to the park with Mike because the yardwork will keep but his childhood cannot, is why she'll end up wondering where the years went.