Every year Joseph, Mary and family went up to the Temple in Jerusalem for the Feast of the Passover. When Jesus was 12 years old, they were coming back from the festival in Jerusalem to Galilee when after a days travel they realize they lost Jesus and spend three days looking for him.
When you only have one child, you don’t lose him. You could say that this is evidence that Mary, by this time, had six other children – when you don’t use contraception and don’t use plastic bottles to feed a baby, women have a child about once every two years.
I think that Mary was occupied with other relatives and children, but she was not giving birth to them. The youngest of Joseph’s children would have been aged about 20 at this time, and the seven others older than this. So Mary was probably taken up with looking after their children i.e. her and Joseph’s grandchildren.
At any rate, Jesus might have been the Son of God, but he was not a spoilt child. He disappeared and no one even noticed he was gone. Jesus had stayed behind in the Temple – which in typical 12 year old fashion he said was his father’s house, as if it were obvious.
The Temple was filled with Mary’s lot: the prophetess Anna was probably Mary’s grandmother, while Simeon was probably Mary’s uncle on her father’s priestly line side. Although Jesus’ great grandmother and great uncle would not still have been there as they were both very old when he was born, the Temple would still be full of people who remembered them and remembered Mary living there as well. When Jesus remained in the Temple there was more of home about the place for him than most people would think.