I have one adopted child, a son, who I adopted at 8 months from a Kazakhstan orphanage & a biological daughter who was born to me in Indonesia. I did not fall in love at 1st sight with my biological daughter. I came closer to having this reaction with my son. I really don't know quite why. There was a difference perhaps because he was older & mobile?
He hasn't always been the easiest child but I've always loved him madly & deeply. It took about a year before he was able to tolerate human touch. And he has ADD so it's been a struggle. It doesn't matter. I love my children equally.
You love an adopted child just like you love a biological child because they are children & need your love. And they love you unconditionally. Oddly enough, in many ways, my adopted son is more like me than my biological daughter. I always struggle to understand why people insist on having their own biological offspring. Things can be difficult in either relationship. There are no guarantees. Both relationships mean the world to me.