Is AUTHOR wrong in the post ? POST : I'm a female and my boyfriend and I are both 23 in case it matters.

I started dating my boyfriend about 2 years ago, right around the time his mother had gotten remarried and was pregnant with my boyfriend's new half sister. His sister was born about a month or two after we were "official". I visited his mom in the hospital after the birth. 

His mom is amazing. She welcomed me into their family with no hesitations. She's extremely supportive, unbiased, and really has everyone's best interests at heart. As someone who doesn't have a great relationship with their mother, the relationship I've built with my boyfriend's mother is invaluable to me.

Now, I'm not entirely fond of kids. I feel like i sort of missed out on some of the maternal instincts I see from other women my age. To be clear, I don't automatically hate kids. I just don't automatically like kids just because they're a kid. That being said, I loved my boyfriend's little sister (I'll just call her Alice). She was so sweet and cute and smart. Think huge brown eyes, chubby cheeks, and dark curly hair with the cutest smile. She's really adorable.

Alice used to be very fond of us as well. We go to their house about once a week for dinner and she loved being held by my boyfriend and me. She was all smiles all the time.

Around the time of her first birthday, the "stranger danger" kicked in. She no longer trusted ANYONE. If her grandmother comes over less than 3 times a week, she won't even make eye contact with her the next time they're together. Its the same with my boyfriend and I. She won't be in the same room with us, she'll barely make eye contact, and she was suddenly scared of my dog (a senior citizen waddle butt) that she used to adore.

I am 100% positive there has been NO abuse if that's what you're thinking. Alice's father tends to be a little introverted and her mother is an "extroverted introvert" as she calls herself. My boyfriend's younger brother is also fairly shy and introverted. 

Alice is now 2, she's been consistently socialized, her mother is the best mother I've ever seen, and i can't see any reason why she suddenly became so shy. Apparently her mother asked the pediatrician about it and he said it wasn't anything to worry about.

So, am i the asshole for losing interest in her? I don't really feel the need to try to make her like me when 99% of the time it just makes her scared. My boyfriend is 100x better/more patient with children than I am, and he hasn't made any progress either. Its been A YEAR. I don't pay much attention to her anymore because I don't feel like getting disappointed when she wants nothing to do with me. 

I feel like this might be upsetting his mom and her husband now. They haven't said anything outright but I've noticed that they might be a little upset that I don't really like her anymore. 

For clarification: I have never been mean or rude to Alice or her parents. Its more of an indifference. I used to try a lot harder, but after a year i basically say hi, smile and wave, talk to her a little bit, then she runs in the other room and hides and that's about where i lose interest. My boyfriend will make a few more attempts than I will but still with no progress. 

Am I the asshole?