Bwahaha. I'm just waiting for the day when Steph and/or Selina is like "For some ridiculously complicated plot reason, I need my baby RIGHT NOW. If only I hadn't put the child up for adoption..." and then Tim and/or Bruce stares at the floor sheepishly and admits that he not only knows who adopted Stephling and/or Helena, but where the baby is right at this very moment, and yes, he goes to check in on the baby every weekmonth, while not following any sort of pattern that a villian might figure out the visiting was deliberate or the house was getting any special vigilante attention. To make sure the kid is safe and not getting raised as a supervillian or anything.
The 'being adopted by the same parents' thing, combined with Tim and Bruce not clicking to the fact that the other one knows where the babies are and checks in on them, and we have a soap opera. They could stretch it out to 6 issues of the Wacky Hijinks of Bats Who Stalk Their Children The Offspring Of Their Girlfriends.
Lian and Sin could guest star as the cool older teenage superheroine martial arts fighters who the new little heroes look up to and train with.