Ooh, this is delightful. I couldn't stop reading this. 'Gus is such a delightful child, and just the way I think he'd turn out with Severus as a father. I saw that you write in another comment that you don't have children; I'm floored! My son's only a baby, but my daughter is Gus' age and you have that age group totally pegged. Very well done!
I normally hate stories that flick between years, but this was done extremely well. It managed to give me backstory, rather than, well, shit me by flipping around. I don't know how you managed to make me like it given how much I normally hate it, but I liked it a lot. :)
The rest of the fic was fabulous as well. I love Harry's devotion to Severus, and Severus' disregard for Harry. Albus' 'resurrection' was fresh and wonderfully played out. I think it was great that you went so far back in time to establish a bond between Severus and Harry. Absolutely brilliant work all round.