Last night I was reading to the kids and my girl asked me what the word "mine" meant. I explained to them that "mine" means "something that belongs to me". Then I gave them a few examples. With kids, I always explain using examples. It helps them to understand better.
I pointed to my pillow and said "This is my pillow" so "This pillow is mine." Then I pointed to the blanket and said "This blanket is mine". Then I asked them to give a few examples and the sweet talker (the boy) pointed to me and said "This mummy is mine." lol