Actually the kink itself was fascinating - entirely due to how well you have written it! If you have an inclination to write more of it, or continue this story, you would have my overjoyed vote to do it!
However what really gets me in this story, is how wonderful Severus is. Loving, caring, indulging, and most of all, supremely understanding. Also, heh, I loved how Harry noticed the effect on Severus when Harry used the word "Daddy". :D
As a matter of fact, when I read this story (before the reveals) I could tell that it had "you written all over it". :D I adore your idyllic Master/pet, or in this case, Daddy/little boy stories. And honestly, having read this story, it truly amazes me that there hasn't been a huge number of daddy kink stories in snarry. The pairing seems to lend itself to it fantastically well!
Sorry to write this much, but this story, and the kink itself, deserved a lot more than a one-liner response.