For beginner campers, there's a bit of a trade-off. On the one hand, there's very little that you actually NEED: a tent, flashlights to find the bathrooms in the dark, first-aid kit. On the other hand, you want camping to fun, not a burden, otherwise what's the point?
So--if the thought of acquiring and using a stove, pots, ingredients, utensils, etc. gives you hives, bring disposables and picnic food. If hot food rather than sandwiches will make it way more enjoyable for your family, then bring a camp stove and pots and pans. But if cooking with limited facilities will drive you bonkers, bring premade reheatable stuff. Etc.
Think about gear or supplies you'll need for activities you'll want to do: swimming, boating, birdwatching or stargazing, hiking, biking, etc. Also allow for bad weather: cards, drawing supplies, board games.
Lots of gear is available cheap on Craigslist.
I hope you have a great time! We've taken our kids camping for years. Now the older ones are married with kids of their own and we all camp together once a year. We have a treasure trove of family lore collected over the years, and the grandkids are getting to hear stories that begin "remember the time when... ?"