Grandson of Bhaal????

I have finished BG2 and throne of Bhaal a couple of times, often romancing Aerie.
I believe in Shadowkeeper, I found the item Aeries baby and now I just saw a reference to it in the romance discussion.
I never seen the baby in gameplay...is there something special that triggers the baby?
I thought I had "finished" the Aerie romance and at the end of ToB I get the epilogue of me and Aerie ruling this or that.....
But the baby......please inform me how to get a baby!!!

(And no juvenile remarks, please ;P)