How old are your kids? If they are pretty young, then you're probably going to want them to catch something quickly to keep their attention. I do this with my 4-year old. Tie a snap swivel to their line and get some pre-tied hooks. Like these: Link to hooks
Then put a small bobber about 12-18 inches above the hook, depending on how deep you want to go.
Then get some earthworms at wal-mart. Try to find the earthworms, not the nightcrawlers. The fish will pick the nightcrawlers off your hook without getting hooked themselves. earthworms are a bit tougher in that regard. Cut a piece of work about twice the size of the hook you are using and thread the hook through the length of the worm. so the hook should be mostly covered by the worm, with the rest of the worm dangling beyond the hook (and hopefully wiggling like crazy).
Go out to a local pond and look for areas where there may be some small fish. Overhangs or near some structure. the worms pretty much guarantee you'll catch some sunfish if they are around. If you find a good spot, you'll be catching sunfish on almost every cast as long as your worm is fresh.