Two interesting pieces of work on the chemistry underlying parental care of children:
Lerch-Haner et al. find in mice that serotonergic function is required for the nurturing and survival of offspring. Mothers with a specific disruption in serotonin neuron development built poor-quality nests and did not keep their offspring huddled together, leaving the litter exposed to the cold. Their litters died within a few days of birth despite adequate nursing. When these mothers' young were fostered by normal mothers immediately after birth, their odds of living rose to normal.
Prudom et al. find in Marmosets (a bi-parental primate) that fathers exposed to isolated scents of their infant displayed a significant drop in serum testosterone levels within 20 min after exposure, enhancing their positive infant care.