I’ve known enough exceptions to believe the answer is “not necessarily” and “it depends”.
a) Is the woman in question the biological mother of the child? Chances increase.
b) A mother but not the child’s biological mother? Chances go down.
c) Not a mother? Chances go down.
Is it enough to say “instinct of women to children”? I don’t think so.
I don’t necessarily think that instinct is valid for most mammals either but socialization, because mammals born in captivity behave differently.