Depends if its the type of camping you park the car next to, or if you'll be lugging your gear across a bumpy field.
If you get air beds, put something insulating on top (like a duvet or folded blanket) to stop the cold.
Sleeping bags and additional blankets.
Hot water bottles.
Gas camping stove, there's all sorts, the cheap ones are fine. You'll need more than one ring if you're doing proper cooking like a fried breakfast. Multiple stoves works well.
A cheap kettle that whistles.
A toast rack thingy for the stove, they're cheap and work well, you can do 3/4 slices at a time.
A light for inside the tent in case of midnight waking/toilet trips. Those bulb shaped ones on a string are good, you can tie them up somewhere and then they're easy to find in the dark.
Wellies/waterproof footwear. The grass will be wet in the morning.
Depending on your tent, somewhere additional to take off muddy/wet gear, so you don't get your sleeping area wet/dirty. A porch attachment or gazebo works well. Put a tarp down to stand on and keep mucky stuff outside the tent.
A table of some sort, to put the stove on. You can eat off your laps, but cooking on the ground is no fun!
Folding chairs. Cheap ones are fine, fold them in the evening to stop the dew getting them wet.
More layers than you think you'll need. It's miserable if you get cold and can't warm up.
A cold box. You can get electric ones if your pitch has a hook up, or you can freeze bottles of water to use as ice packs. You can drink them when they've melted.
Some campsites have a freezer available to refeeze ice packs.
Plan food that doesn't need refrigerating. Tins, and jars. (jars of hotdog sausages are good!)
Something for the kids to do. Swingball, or a pop up badminton net or something to keep them occupied - especially while you put up the tent.
Practice putting the tent up before you go! You don't want to get stressed out or realise you're missing a pole or something!