Yeah, I think people will definitely have nostalgia for these days of itchio in years to come (especially if this is where they started off with games) and we'll look back at the current indie scene with fondness. After all, there's nostalgia for the early days of Newgrounds flash games and- going further back- the ZX Spectrum bedroom programming scene.
For kids, I'd put Baba is You on the curriculum as a good demonstration of logic.
l really agree with your opinion about itch.io been flood filled with horror games, l also don't like that. It ruins all the other beautiful games that are hidden on this site.
About that first game, this question isn't that easy to elaborate because it's everyone personal opinion, but that first game wouldn't even be an itch.io game, it would be Tomb Raider :) They say start with baby steps and in reality l agree with that. Anything on the internet, even this "platform" might become dangerous for younger existences as they don't know how to protect themselves and might result into the exact opposite you wanted to happen. So imo the best way to handle the situation is by NOT allowing the children to reach the internet by themselves. (Kinda got out of the theme but l think l do make some point).
So you've been away for a year now, that's good, don't let it take your quality of life.
In my time as a kid there was no itch.io nor any online indie game dev. community, internet was barely a thing back then, so I played genesis and N64 all days with my friends or solo, until I started digging into making games myself, so I kept it balanced between playing and making. So I could somehow make a relatively healthy habit out of it (for a kid :D).