We had our eldest in the tent at 10 weeks old and 12 weeks with the boy. They are 13 and 5 now and both just treat camping as something they “just do” – we kept them warm with a proper sleeping mat and wedged in between us with a kids sleeping bag. The eldest spent her first nights camping wrapped in a down jacket!
The main thing is to just treat it as a normal thing, don’t let them set the agenda, stick to a similar bedtime as at home and if they do kick off use distraction etc. We have stuck the boy in the car at 0500 and gone for a drive to lessen the annoyance (bit of a rare one that).
It’s very much a case of making it “normal practice”. We also find that going away with other friends and their families helps; more experienced kids help the noobs settle in.
Good luck and keep it up.
Chris