Babies want to be Close to their Adults

And Adults want to be close to their Babies.

It is not unusual, down here, to see a woman holding a baby (or a young child) in her arms, while walking down a road, or taking care of her household duties. 

In Primates, our close relatives, babies ride on the backs of their mothers, holding tightly to her fur.

Human babies have retained the ability to clutch anything put into their hands. And can be lifted by their arms when changing diapers.