Tip 1: Leave them home!
Ok, joking aside, this was my situation exactly 2 years ago when I surprised my wife on our anniversary with the new trailer in my signature. My kids were 5, 2, and 1 at the time.
Our first couple of trips were planned very close to home (about 1/2 hour drive) for the convenience of leaving something behind. It worked out well as we never had to return home. As many new RVers do, we overpacked. But it thinned out over the coarse of that camping season.
By the end of the summer, we were comfortable enough with the TV and trailer that we took a 1 week trip down to Florida and camped at Disney's Fort Wilderness. Wonderful trip it was and now we plan for it each year until the kids grow up.
So in summary, you'll grow into the role of RV camping family. Your needs will change as the kids get older. Pack'n'plays work well at 1 and 2 years of age, but tend to be cumbersome as they get a little older.
We did buy a "Children at Play" sign and place at street side in front of our trailer as some folks push the speed limit inside the park. If you can find one, they work well as I see drivers being more attentive with brake lights on.
Other tips: smores, campfires, hobo packs all make for great night food and entertainment. Fans are wonderful "white noise" makers during nap time. And bring tons of glow-in-dark sticks, bracelets, and necklaces. They are cheap, always a kid pleaser, and your children will make friends very quickly with them.
Good luck, have fun, and enjoy the many years of camping memories you'll make with the fam.