After the sixth tiny, force-sensitive child Din brings to him, Luke despairs of ever convincing Din that maybe every single unattended child you meet doesn't need to be adopted (which is really a difficult argument to have, since Luke genuinely agrees that in all six situations, Din had been justified in removing the child). It's what he gets for agreeing to train (co-parent) the first child and then becoming best friends with a Mandalorian, for whom adoption is apparently an imperative instilled in their very being. As he watches his strange little family grow, he does wonder why Din keeps bringing the kids to him before remembering when he used to tell his Aunt Beru that he wanted to have a lot of kids when he grew up but didn't ever want to get married and how he may have told Din that story a few months after they met (when Grogu was still an only child) and his heart swells with love for his best friend.