Nintendo is better at couch co-op or split screen games. Anything Mario (e.g. Kart), the common casual games (Overcooked), etc. And these games are easier to setup in split-screen mode. The Deck is awesome but 4 Bluetooth controllers is super painful (which one needs re-pairing? who's on controller #1?).

The Deck's wider capabilities (emulators, Minecraft) are also harder to setup and use for kids. The Switch is way more limited but little kids perhaps deal better with a flat "no" than a "maybe, you'll need to work for it".

I think GP's point holds. I'm loving my Deck but my kids are more drawn to their Switch, the Deck intimidates them.