If you don’t want to shell out for some outdoor heating, a quick fix is to provide blankets.
Put a basket full of all your blankets, by the back door with a little “take one” sign, and your guests can grab one to snuggle up in as soon as they start to feel the chill. You can even throw in any spare gloves, scarves and hats you have.
If you have a trampoline with netting, you can drape blankets and sheets over it and cushions inside to make a cosy den for the kids. String fairy lights up inside to make it really inviting.