Xss with gamepass. Absolute no brainer. They can jump around from game to game.
As a longtime dad... I disagree with this one strongly. I'd say that "
they can jump around from game to game" is exactly what you're trying to strongly
avoid with a system purchase, possibly above all other considerations.
Jumping around from one game to another with little investment is what you get on platforms like the iPad--it's basically the perfect recipe for kids to do absolutely nothing but download new shiny items all day and never get past the very first serious challenge they encounter.
The key thing you want to develop as a parent is long-term investment in things, robust endurance when a game gets hard, and the exact opposite of a disposable attitude towards media and content. Make them want serious games that have lengthy value (eg. BOTW, perfect for kids since it has higher tiers of things to do as they get better), let them ask for specific games or save up for them, then have them experience gratitude towards the ones they actually own. None of this games-as-mindless-netflix nonsense that unfortunately is part of the same brain melt happening on all platforms to the current generation.