When Did I Become Mom?

I enjoy being "Mommy".  I do.  Not to mention I'm pretty good at it.  Don't get me wrong, I'm not supermom or anything, but, I do alright. 
Okay, decent.
But I'm not just any old mommy.  I'm still pretty hot.  I'm stylish and still pretty hip.  I might not be at the club, but I at least know what they're listening to.  Dance music anyway.  I gave up on hip hop. Commercial hip hop.  I have awesome taste in clothes and still wear a size small (not bragging, just saying).  I may actually be the youngest Mommy in M's nursery school class, and I like that. 
Being a mother sometimes can make you start felling a little old.  You know, like when your kids are at the age when they call you "Mom", or "Mother"?  I remember calling my mom "mother".  So impersonal, but it made me feel grown up.
I'm grateful my kids are still young and call me mommy, which makes me feel younger.  It wasn't until a few days ago that I noticed my little world was changing.  Now, I've already said M was smart, like 3 going on 33 smart.  He's already at the ask questions about everything in the world phase and has me constantly on Google because I don't have enough brain power to store all the random knowledge  his line of questioning requires.
It was me, M, and his grandmother on our way home one evening and M asked me one of his random questions, and he ended it with "mom."
My MIL looked at me quizzically and asks, "he's calling you Mom now, when did that happen?"
That's what I'd like to know.
It feels like just yesterday I was mamama to him.  Now we're on a one syllable basis?  What is that?
Now, because he's feeling big for his britches, I have to be "mom".  Not cool man.  Not cool.