My guess is that the mother was domesticated at an early age as well.
It's not that out of the ordinary when you think about what's going through the mind of the mother.
Hairless Ape (HA) comes in and gives me food.
HA grooms me.
HA plays with me.
HA is warm.
Trust is gained.
People really underestimate animals...they're not all programmed like mice to simply hunt hunt hunt hide hide hide...