The short version: under the guise of a drawing contest, Google is asking parents to give up their children's social security numbers, place, and date of birth. If you missed it your bank and insurance company are no longer allowed to gather this kind of info, because of fears of identity theft and/or misuse of personal information. But somehow Google thinks they're different.
What could be wrong with filling out a few entry forms?
A national, commercial database of names and addresses of American children, especially one that includes their dates of birth and SSNs, would be worth many millions to marketing firms and retailers.
Of course, data collection is not the reason Google gives for doing this competition. Their FAQ says it's because "We love to encourage and celebrate the creativity of young people..." etc. If that's so, then why on earth would the contest's original Parent Consent Form ask for the child's city of birth, date of birth and last four digits of the child's SSN? Along with complete contact info of the parents.
You see what Google knows and many parents don't know is that a person's city of birth and year of birth can be used to make a statistical guess about the first five digits of his/her social security number. Then, if you can somehow obtain those last four SSN digits explicitly -- voila, you've unlocked countless troves of personal information from someone who didn't even understand that such a disclosure was happening.
This kind of data can be linked with other databases to target advertising. It's worth many times more than what Google will spend on prizes (each State Finalist gets a T-shirt!).