Many Hindus believe that parents should make that same sacrifice to God on behalf of their children, and so many children have their heads shaved, and all the hair is offered to God. It is the child's first act of prayer, obeisance to the Almighty.
Rather than the usual venue at the temple, our sacrifice was done at a Cartoon Cuts... an ingenious salon that features a small tv set at each styling chair for the tiny patrons. My daughter sat through it quite happily, squealing "Scooby, Scooby DOOO!" The stylist was very good about harvesting each and every hair, and handing it to me in a sealed envelope.
My husband's reason for wanting this done is entirely religious.
My motivation was to prevent twenty years of criticism of the texture and abundance of my daughter's hair.
In India, nearly every one is a mother-in-law and many "aunties" who I do not even know have urged me to get her head shaved, so that it gets replaced by a stronger, thicker thatch of hair. I do not want to hear, over the course of the next twenty years, that her hair is not up to snuff, and that I should have had her head shaved when she was younger. That is what assuaged the pain as I watched my baby's head become denuded.