My dck call me by name but when my own were little and called me mom many of the younger daycare kids did too. It is something I kept to myself and didn't seem to confuse them in the sense of calling their own mom mom. Many little ones have the notion that all men are daddies and all women are moms so guess that sort of went along with it. By 2 1/2 - 3 I always corrected them. Even then a child excited to tell you something will say mom. It happens with school teachers too - they get mom and we get Mrs. ...... especially when they first get home and have more to tell about their day than their little brains can hold.