Congratulations on the new little one!! How wonderful for the both of you!!
I know what you mean about that instant connection! I got Cooper when he was 9 weeks old, and the very second I saw him, that baby was mine. I fell in love that very second and that overwhelming feeling has never changed. He is my joy.
I got Carley at 6 months old. She was kinda-sorta a rescue. I thought she was adorable and was more than ready to add her to the family, but that instant connection I felt with Cooper wasn't there. I don't know if it was because she was not a baby, or what exactly...and it wasn't that I was sorry I got her or didn't love her.
It took me about 3 or 4 months actually to have that total in love feeling with her. She kinda felt like a "loaner" or something, and I can't tell you why that was...but now, she is sooooo much a part of the family, she is my baby girl. Believe me that feeling will come for you too!!! I still sometimes feel guilty I didn't love her "as much and as soon" as Cooper, but I try to remember we can't dictate our feelings and I never treated her like a "stepchild", LOL!!
Again, congrats on the new one!!