Where do you live? What do you want to fish for?
For kids I recommend finding a place with bluegill for fast and easy catching.
I can't echo Belem enough. My best fishing days with my kids when they were little, I never even got my own hook in the water, between getting fish off the hook, putting more worms on hooks, untangling lines, etc. And it was the best...we'd find some spot where they could just pull out a bluegill every few minutes.
If you want to stalk a trophy bass, go yourself. With your kids, all you want is bluegill on hooks.
A few suggestions...
No need to go buy a $60 ugly stik or something...anything a little kid can catch the first time they're fishing, they can catch on a $19 rod from Walmart. Would suggest getting the one with the spincast enclosed reel and the push button. The first times you're taking them, you're not there to teach them to fish properly, you're they're to hope they like fishing. If they really like it, then you can start upgrading equipment, teach them to use a spinning reel, etc.
Look for a pond, not a lake. You might get lucky on a lake shore, but often its a total strikeout. You almost always want a pond. Do a search for "Kids Fishing Derby" near you, and see where the last one was, then go there. They almost always stock those ahead of the fishing derbys, so even if you're going months later, at least you know there should be some fish in there. Also, I don't have access to farm or private ponds, so I've found the best luck with ponds behind office buildings and corporate parks. If you find a good one, it so far exceeds ponds in local parks or whatever. I would strongly suggest if it will be your kids first time, make a trip or two yourself, both the get refreshed with everything, and test the pond. For me, it's worth it to know you've got an active spot before your kid's first trip, it's not an exaggeration to say their first time out might literally determine whether they ever want to fish again.
Also, a little kid doesn't care about catching a big fish. They care about catching lots of fish. A kid will have a much better day catching 8 or 10 3oz bluegill than they will catching one 10lb bass or a giant catfish. Don't worry at all about finding a place with big fish.
I still find nothing does better than a nightcrawler, and its worth dealing with the grossness of it. It catches pretty much any fish in the pond, and it stays on the hook a long time. Any kind of bread bait or chicken livers, you will be replacing it every couple casts. Kids don't really sit with their cast in one spot for 30 minutes.
Maybe controversial, but if your kid has a decent amount of focus and can be trusted to hold the rod, I would suggest you skip the bobber and teach them to feel the bite and set the hook from that. The bobber sounds great in theory for kids, but expecting a kid to stare at a bobber without looking around is a big ask. But if they will hold the pole, they can look all over the place, and they'll still know when they have a bite. I also think they'll be better sooner at setting the hook. I skipped the bobber with my girls, and they got good at setting the hook and catching the fish at a pretty young age.
And after all that, don't feel bad if it's just not for them. My two oldest were girls, and they loved to go fishing any chance they got. Just a pond, worms, mostly bluegill with an occasional catfish. They still fish occasionally as adults. Fishing with my little girls is literally some of the best memories of my life. My son was the youngest, he was brought into it exactly like them, went fishing with them and myself, caught plenty of fish...and just couldn't care less. At best he'd be done in 20 minutes, no matter what he caught. And he's an outdoors, camping, boy scout type kid...just didn't enjoy fishing.
Honestly, it was a big kick in the nuts, because I just assumed I'd have "fishing with my kids" for another 5+ years or so than I did. When the girls kind of aged out of it in high school, my son had no interest, and it was over just like that.
