Choosing a sleeping bag is next in importance after your tent. Like your tent, your sleeping bag can be one of many types depending mostly on personal preferences and outside temperature. The shape, roominess and fabric feel should be tried just as you would try out a new mattress at home. Sometimes the weather will be warm and dry, so you might not even need a sleeping bag, just a light cover as you would at home. Other times, the cool night air will dictate a warm bag or combination of warm clothes and warm bag.
Style and Shape
Unless you are backpacking where weight is the overriding factor, you can choose whatever shape you like. Most manufacturers offer two basic shapes, rectangular and mummy, plus some variations of each.
The most common sleeping bag is the rectangular style. It is roomy and comfortable inside, and can be opened and used as a comforter on warm nights. Many rectangular bags can be opened and zipped together to make a double size bag – great for very young kids and especially good for parents!
The mummy style sleeping bag is meant to wrap tightly around the sleeper, so it will provide maximum warmth while using less material. If you will be camping in cold weather, like 40 degrees and below, you might want to consider the mummy. This efficiency will also keep the bag's weight to a minimum, making this style the choice if you will be backpacking. Not everyone likes the confines of the mummy, so you might want to try one before buying.
Variations on these include the "barrel" shape, which is a mummy with extra space in the middle. This is a good compromise if you want a mummy's warmth but need a little space for comfort.
All styles of bags can be bought in three lengths, junior, standard and extra long. The juniors are for small children. If weight is not important, I suggest you get a standard length for your child. The bag will last many years, and a junior size bag will soon be outgrown.
The extra long size is usually advertised for those over six feet. However, the extra length might be appreciated by shorter persons. It just depends on what makes them most comfortable.
Another dimension to consider is the girth. Girth is the inside space, as measured around the sleeper's waist area. As noted above, mummy bags have the smallest girth, and rectangular the largest.
Temperature ratings are often advertised by manufacturers – 0 degrees, 20 degrees, 40 degrees, etc. Consider these as guidelines only. You may sleep warmer or cooler than someone else. These guidelines seem to assume that you will be wearing warm clothing too. You can probably use any bag rated for summer temperatures as you start out, since you will most likely be camping during the warmer months.
There are several ways to make a bag warmer, other than wearing warmer pajamas. One common way is to use a “liner” bag. These bags are placed inside you regular sleeping bag, like adding an extra blanket to your bed. You can buy these bags ready made, or make one by attaching a blanket to the sleeping bag with safety pins. You can also just through a blanket over the top of you bag, rather than put it inside. When it is really cold, two summer bags can be used, one inside the other.
Moral of this story – it's easy to make a sleeping bag warmer, so start with a warm weather bag like a 40 degree rating or warmer depending on your location.
Once upon a time the good bags used prime goose down for insulation. This is still used, mainly in the highly specialized mountaineering bags where extreme dry cold, and light weight are the primary considerations. Down's cost and difficulty in washing make it impractical for most camping.
Actually, modern synthetics have been developed which have all but replaced down. Synthetics cost less, are washable, and can be nearly as warm as down, especially when it is damp outside. For most family camping situations, most any of the synthetics will be sufficient.
Zippers and Collars
You should be good quality, and should not pinch or catch on the fabric when zipping up. You should be able to zip it up from the outside or inside. If you plan to connect two bags together to make a double sleeping bag, make sure the zippers are compatible.
Some bags have a collar at the top that helps keep the opening closed around your neck to retain heat. This is useful in cold weather, but is unnecessary and perhaps annoying, in warm weather.
Choosing a sleeping bag is really easy. In fact, you might not need a sleeping bag at all! Plenty of campers started and continue with a bedroll. You can make your own bedroll by taking sheets and blankets and making up a bed just like home. Add more blankets or a comforter for cooler weather. It will be best if you have some sort of mattress to make your bedroll on, like a futon or air mattress.