Getting the current version:
Pro - there’s a massive library of games and services that’ll work great for what you need it for
Con - any new games won’t be available, and the online services maybe shut down in a few years as user move to the new software
Waiting for a new one:
Pro - you’ll get all of the upcoming games and the new one is going reverse compatible, so any old games should work perfectly
Con - waiting another year. It’ll be more expensive.
Your kids would only play Mario and stuff now, but game systems have a lifespan of 5+ years, so you might wanna think about what they’ll like in a year or 3 down the line
Also. Basic kit for new switch users with younger kids
Mario Kart
Kirby Star Allies
Zelda Breath of the Wild / tears of the Kingdom (for the older ones)
Luigi’s Mansion
Mario Wonder
There’s also an online subscription that’ll get you access to a library of old retro games from NES, gameboy, n64, etc
Any combination of those will work fine