They stole the idea from a Tumblr created in March:
http://fapfapfapworthy.tumblr.com/ Upworthy staff tweeted it out back in March and then again last week. Pornhub favorited that tweet and then decided to steal the idea. Proof: https://twitter.com/AndreaGarVar/status/494806824365723648
Response to Show Us Your Cutest Childhood Photo:
Guess what day this was?
Wrong, it was Christmas.