There’s always been this fandom-wide headcanon that Grantaire’s good with kids, and he generally gets assigned the role of Gavroche’s protector in the musical. (Although Courfeyrac got it in the movie.) And he knows about different types of Paris gamins, and he offers Gavroche’s friend Navet breakfast and refers to him by name when he’s left. And then I ran across this, in the middle of one of his epic rants (bolding mine as always…):

It’s like children, those who want them have none, and those who don’t want them have them.

Which I think is translated differently in other editions, so for all I know that might not even be what he’s saying. And of course he may not be referring to himself (although I like to think the second part is a reference to the Thenardiers), and oh god no he wouldn’t be a good father unless he cleaned himself up. But hmmm…food for thought.