On the purely economic level, Google is offering a hunk of electronics and software for $250. (There are secondary economic effects too; the Chromebook will encourage the use of Google services, etc).
On the emotional level, Google is offering an an experience and trying to show how it could be a part of your family life and make it better. And you are offering Google employees a chance to feel like they're making the world better (speaking as a Googler, I can say that I definitely care about that sort of thing).
As a completely honest question: do you feel this way about ads that sell diapers/baby-food/etc?
ps. Congratulations on fatherhood!