As many a Kodak commercial makes clear, child-rearing involves plenty of cuddles, angelic smiles and moments of treacly sweetness. But parents know that raising children also involves those other times — when the bowl of oatmeal overflows in the microwave while you resolve a sibling quarrel, when your knuckles whiten as you grip the dashboard for your teenager’s first highway drive, when you try yet again to encourage a child who is struggling with the intractable mazes of geometry.