Poles are such an integral part of skiing that the sooner you get used to having them in your hands the better, even if you are not immediately ready to do pole plants. Poles can help you balance when resting and standing, they'll make getting out of your skis easier and you can use them to push yourself forward in the flats.
Opinions on this differ, but in my opinion, kids need ski poles sooner than later. Once the first controlled wedge turns have been mastered, poles should be introduced. Kids poles are generally more basic than their adult equivalents. For example, in some poles you'll find the adult version's handgrip to be made of a more complex two material construction, while the kids version only uses one kind of polymer. And kids poles are a lot cheaper. The reason is that kids will outgrow their poles quickly, and why spend a load of money if you need to get a longer pair the next season anyway. Some poles reviewed here are length adjustable, which means that your kid will be able to use his or her pole for several seasons.
When buying poles for your junior you should keep a few things in mind. Poles should be the right length. Skiing with wrongly-sized poles can negatively affect skiing technique. Poles should be lightweight. Heavy poles are exhausting to carry around and make it difficult to move fast on a pole plant. Additionally, the pole shaft should be at least somewhat flexible so using it won't put strain on shoulders, arms, and elbows. The handgrip should be comfortable to hold and provide a good, non-slippery grip. Bring their gloves along when trying out new poles in order to get the best idea of how the pole will feel in their hands when skiing.
Generally, fiberglass, graphite, and composite ski poles are the best choice because they are lighter and more flexible. Aluminum poles are cheaper, but often thicker in shaft diameter, and can bend and break more easily. The thicker the pole, the more wind-drag it will produce. You will find aluminum to be the most common choice for children because it is cheaper; however, as you will see in this review, there are companies that make composite poles even for their Junior line. The aluminum poles reviewed here are all made by great companies and are built to the highest safety and durability standards.
Most poles come with average-sized baskets to be used on regular, groomed slopes, but some models allow the ability to swap baskets for a day in the powder (for which you would choose a larger size basket).