Kathleen also gave her parents a lot of problems back in the day, with the girl getting two DUIs, stealing Elliot’s credit card, and even getting arrested for robbery and breaking and entering.
It turned out that her issues were probably due to her previously undiagnosed bipolar disorder, and once Kathleen began treatment she was able to turn her life around, helping Elliot and Olivia with a couple of cases and becoming and advocate for sexual assault victims.
Basically, either of Elliot’s kids could easily be in the line of fire when it’s time for us to see them again on Law & Order: SVU, and one of them (or Kathy) being killed is definitely the kind of thing that would convince him to return to the police force.