We put our tent up in the garden every summer and "camp out". It's very good.
The biggest thing I find is that we are much more comfortable sleeping if we have a duvet from home both above and below when we are asleep, even though we also have a foam bed roll on the ground and a winter sleeping bag. Somehow the extra weight and heat makes a massive difference. I'm not sure if that will fit in your car though.
We use two trangias for cooking, but if you are not planning to do a lot of cooking, that will be easier.
We have the collapsible washing up basin, which is very useful indeed, and a big plastic container for fetching water. tinyurl.com/2yc9fp85
We have a wheelie trolley for bringing everything from the car to the tent location as it really can be quite a lot of stuff.
It's all such a lot of stuff isn't it?
Last time we went camping it got terribly hot and I got a headache from the heat. The solution turned out to be a bag of frozen peas to wear on top of my head. That really was very nice indeed.
We usually take a lot of tinned and packaged food that requires no cooking or refrigeration. That is easier. Food that you can eat straight out of the pot is also handy, like rice or pasta.
Lots of string so you can build camp gadgets.
Hats with broad brims are a good idea for preventing sun burn. Like this:
https://www.alpinetrek.co.uk/outdoor-research-sombriolet-sun-hat-hat/
The ladybird book of camping is very good.
https://www.ebay.co.uk/itm/335118850358
It has some guidance on how to build camp gadgets.
Good idea to take stuff to stop the pain of insect stings, like bee and wasp stings. And savlon and plasters in case of thorns and whatnot. Also thermometer and calpol.
Also some very soothing and ultra reliable activities that one parent can do with both kids, if the other parent is going round the bend from tiredness needs to relax for a moment.