Carabiners are metal loops, vaguely shaped like a D, with a sprung or screwed gate.
You’ll find that hooking a couple of them to your back or fanny pack useful in many ways. For example, if need to dig through a fanny pack, you can hook the strap of your trekking pole to it. Your hat, camera straps, first-aid kit and a number of other objects also can connect to them.
Hook them to your fanny pack or backpack upon purchasing them, so you don’t forget them when packing. Small carabiners with sprung gates are inexpensive, but they do have a limited life span of a couple of dozen hikes.
Read more about day hiking with children in the guidebook Hikes with Tykes.