Playing a stage 1 deck is probably the way to go.
If you're playing kids, you'll likely want a deck that they can look at and go "Wow, this seems cool. I wanna try it!" and still be able to understand what's happening, while also exposing them to the various nuances of the game.
So... A simple and easy to copy engine is probably a good place to start. Claydol + tons of trainer engines are fairly easy to make, fairly simple to understand, while being effective, and similar to what people actually play.
I'd... Stay away from stage2 decks and fossil using decks, as those can be a tad disorienting (fossils in particular are weird with the trainer basics, and stage 2s require players to be more familiar with their evolution lines then stage 1s do).
So a stage 1 deck is the way to go...? Something that showcases special conditions, stage 1s, favors good set up (getting multiple weezings out, gets them used to idea of setting up cards), and gives them a type that is super effective against a popular deck is a poison deck (Toxicroak, Weezing, Arbok if you really want, but is not needed as much).
Actually, Floatzel GE and something like Octillery would make for an interesting deck as well, with demonstrations of damage spread (Floatzel), countering (Octillery's first attack countering special energies), and the deck is open to include Empoleon (DP Empoleon is similar to Floatzel, which they'll be familiar with playing, and of course the same type) when kids are ready for Rare Candy tricks and more complicated pokemon lines.
Just two ideas there. I WOULD however try to keep them using trainers that are using competitively (like the Balls), rather then stuff that's never used (like Potions), to keep them used to the methods of getting set up (pokemon search and draw cards). Sure, if the kids can't read yet, something such as Galactic's Wager might be a bit much, but cards that are simple yet effective like Pokedex and Great Ball will be very useful.
