The health bar is made of increments of 5, and a successful feeding at best heals a villager by 1 point. If the garden is done, I also like dumping villagers there so they enjoy it--they take a nice, leisurely walk across the village, so it allows them to naturally heal a little bit without plunking them on food bin repeatedly. Unless your village is suffering from starvation, mothers and kids will eventually heal up a bit barring any illnesses that may afflict them. Oh, and note that if the health "mercury" is totally within the left-hand bulb, that the villager has 5 health or less!