Keeping warm while sleeping under the stars is essential. If you have to carry all your equipment, then invest in state of the art sleeping bags.
Some of these are designed to cope with arctic conditions so a cool mountain range in summer is a breeze.
Before it’s time to sleep, a well built camp fire will keep out the cold and create a good heart for the group.
Ensure that all embers are totally out before moving on, in dry areas fires are a real danger.
If you have a car to load up and your tent will be pitched in a camp site then keeping warm is a lot easier. Wear clothes in layers, it’s less bulky and your body heat is retained much easier.
An airbed will keep you off of the ground, which is better. A more basic sleeping bag will suffice if you remember to pack plenty of blankets in the car. Never be tempted to zip sleeping bags together, they are designed for one, and sharing only ever results in an uncomfortable nights sleep for both parties.
Actual heating can be taken along to a camp site; there are plenty of portable heaters available. Be careful of safety especially if you have young children, it might be easier without them rather than spending time worrying.
Real fires are usually banned at most camping facilities as they can be a nuisance. If you still want to use a fire, you will probably have to buy an approved product rather than a natural open fire.