The altricial needs of human offspring are demanding, especially in their earliest years. So, to encourage their keep, babies are designed to look adorable.
An infant’s head is proportionately large. The eyes are significant saucers in the center of a plump face. In absolute size, children have larger pupils than adults.
Limbs are short and fat. All told, babies look like disarming cartoon characters.
Infant smiles and coos are affecting. In contrast, their cries wrench compassion from caretakers. If not, wailing away drives an adult to distraction, provoking action to pacify the racket-maker.
Baby babble and crying is compelling partly because it is done in the mother tongue. Babies cry in melodic and rhythmic patterns that they have learned since womb-time.
Babies have another, most important, advertisement. They tend to bear their father’s visage more than their mother’s. This is consistent with other mammals.
As dad is less inclined to care for a tyke, a baby that looks like heritage incarnate acts as inspiration for attention from a man who cares his legacy; further proof that evolution is adaptive, sometimes manipulatively so.