Small crappie type hooks, worms and minnows are a perfect start and introduces them to handling baits. The minnow's are much more fun than worms (or at least with my two boys 7 and 2).
From the bank/shore/dock the easiest thing is just put on bait on a small hook and use a bobber.
Sometimes to help get action to the bobber,,, (if there's no birds around), crumple up some bread and throw it in the general area...
Keep at it and during the non-fish catching "boring" time... that's the perfect time to talk with them and also pick thru tackle and all that... Dadda has to keep a sharp eye out though on that bobber!! Kids will find something other than watching the bobber rather quickly.
Another tip to help keep their interest peaked is, the occasional tossing of a small stone in the general vicinity of the bobber to make it "appear" a fish is near....


(note- they catch you doin it.. yer busted for life!! so be sneaky)
When they do catch a fish... WHoop it up!! no matter what size!
Good luck and anytime you can take a kid fishin... it's all worth it!
here's my current crew of 2 fisher pix: