The first and foremost importance is the material of the sleeping bag. Generally children sleeping bags are made of synthetic polyester and cotton fills. Fleece is also an excellent alternative. It is to be noted that, children skin are highly sensitive, buy a sleeping bag that is hypo allergic and non-reactive to the skin.
Another feature that needs to be considered while buying a sleeping bag is it should be safe and secure. Make sure the kid does not end up covering his face while sleeping. The sleeping bag should have a neck hole to provide ventilation, even if he covers up his head.
Children have the tendency to loose body heat easily and vice-versa. Make sure the head cover of the sleeping bag is replaceable to enable the child to remove the head cap easily as and when required.
Kids love colour. Try to buy a sleeping bag in animated prints with colourful hues to appease your kids. They will make your kids love their sleeping bags. Another reason for buying bright coloured sleeping bags is it provides complete visibility of your kid while on camp at night and in diffused light conditions.
Lastly make sure to buy a sleeping stuff that is light and flexible. This is to ensure that the children can carry their sleeping bag on their own while travelling. Then, children have the tendency to carry a lot of objects while travelling such as chocolates, toys and others. The sleeping bag should contain numerous pockets to help the kids carry the needful.