To those who identified the issue as being general favoritism, you are absolutely right. Several years ago, one of my sisters (I have lots) came home after living out of town and not being home for 3 years. She quietly asked me if it bothered me the way I was being treated. Everything I said or did was brushed off. To be honest, it didn't at the time because that is simply my role (ie, invisible until something goes wrong, then visible as the source of the problems).
My mother used to make a comment when I was a kid about "why are you always there whenever there's trouble?" I couldn't answer that. But it seemed to be true. If something dropped or fell or went wrong, I always seemed to be in the room, ergo I always got in trouble even if it was not my fault. It bugged me as a kid, but I just sort of reached a place where I didn't notice it anymore. It hasn't impacted me much except that I'm prone to apologize for things that aren't my fault. I say sorry way too much. But that aside, I really stopped noticing it.
Mr. K thinks that there are some subtle racial issues at play, like my parents just expect my kid to be smart because he is of an ethnicity that is stereotyped as smart.
I couldn't really tell you why it's happening. But it bothers me.
To stop the aggravation, stop talking about it. It's not a competition between your child and your sibling's kids. When your mom talks about the other kids, be excited for what is going on in their lives don't compare it to your child.
I just want to clarify this point, as it's come up several times in various ways. The issue is not just with my mother, but her examples are the easiest to follow as one would expect a grandmother to be interested in her grandchildren - all of her grandchildren.
It's not a competition. And I'm really happy for my sister's kids milestones. In fact, she and I would talk at length about her kids before LK was born. I got to hear about every first. The first smiles, the first words, the first steps, the first everythings. I enjoyed it and still do. I went back and looked at my old chat logs with that sis and found that she would talk to me daily about all the things going on with her kids.
And then LK was born. At first, the conversations were similar - a back and forth of LK's developments and her kids developments. Unfortunately, LK began to overtake one of her older cousins in certain milestones and then the conversations stopped. It's not a competition, but it would be nice to be able to talk to my own family (namely, my sisters and my mother) about the exciting things going on with LK, just the same as we talked about the exciting milestones for my neices and nephews.
So there are probably lots of underlying psychologies that could be discussed. But this is about the etiquette of the situation and finding a polite way to say "Hey, I am not a liar, I don't like the insinuation, and it would be nice if you could recognize this little member of the family as being capable of some pretty incredible stuff*."
*I can give non-vocab examples, but I'll have to do that later, as she is being a little naughty and needs attending to.