If that was the campaign they ran for the Google+ Photos feature launch in 2012 (when they released Photos before making it standalone in 2015), the other part is that the campaign encouraged people to take pictures of their very young children in order to catalog their life.

Then, their Google+ architecture allowed random people not part of the family group to view said photos of people's very young children, and it got a round in the tech news cycle. They started tightening up the architecture and in the process decoupled it from the dying Google+ to go on to release it in 2015.