I'd got for inflatable mattresses if I were you - they are pretty comfortable. Get the ones that plug in and inflate themselves.
Torches or camping lanterns for if you need to go to the loo in the night.
Adapter so you can charge a few different devices at once.
Kettle, and pot noodles if you like them!
Stuff to keep the kids (and yourself) entertained - tablet you can stream films on if you do that, games like top trumps, travel versions of games etc, plenty of books, colouring or stickers if that suits the age of your kids. .
My daughter (older teen) brings craft projects to do in the evening! (She is more organised than me!)
Hoodies, joggers, easy to slip on shoes like crocs.
Have fun! I have been taking my daughter camping since she was about 6, and we still go together now. We usually go in a pod as it's less stress than a tent, and you get a plug socket, light, usually a heater....
This thread is making me want to book to go over the summer .....