More pronoun fun

Just because I am currently obsessed with the toddler acquisition of pronouns, I had to share this. Many of you are familiar with the kid gymnasium chain called MyGym. Well, as far as Seth is concerned it is now Mommy's Gym. Most recently he was perfectly happy calling it MyGym. Originally he called it MyGym, and then for a little while he called it Seth's gym, and I corrected him, no, its MyGym. So now of course, it is Mommy's gym and I cannot convince him otherwise. It always astonishes me what they connect on their own. I forgot to mention this in the Mysemite post, but he has for a time now said Mys instead of Mine, and I couldn't figure out why until I realized he was connecting the opposites i.e., your is yours, therefore my must be mys. How does anyone ever learn this language?