Whats in a name

My 3 yr old asked me today what my "normal" name is. You know, Not mommy. I told him Michelle. So he says, "Michelle Mommy?" As in mommy is my last name. I told him no, my last name is the same as his. He asked why he calls me mommy then. I explained that its the same reason I call him Son. He understood that, which honestly surprised me. He said, "Oh like I call ds5 my brother." Then he continued, "Hes also my friend." How sweet is that?