"Something only dad does best is play and have unstructured fun," said Christine Carter, a sociologist and author of "Raising Happiness." "That's how kids learn to interact and follow direction, and kids know dads can make mom happy."
A happy mom means a happy marriage, and sociologists say that it's important for kids to live in a stable home.
"Good old dad represents the downtime we long for," Carter said. "He's the easygoing, playful, teasing love in our lives."
He can be the love in our lives that holds our hand as we take our first steps, and when we're older, that holds our nervous arm as we walk down the aisle. He's the humble man of the house with few words but infinite love.
At Roosevelt Hospital in New York, new fathers held their newborns for the very first time.
"When the doctor raised her up, it was just breathless," said one new dad of his daughter.
Another dad said, "I think the best part about being a dad is this -- being able to see someone who you helped create."
It makes one wonder why they call it a maternity ward when dads beam so proud too, filing memories away in the heart.