This padded boys gilet is reduced from £21 to £10 at Next right now.
It's currently available at this price in the following sizes: age 12, 13, 14, 15 and 16.
There are very few details about this item on the Next website, and as you can see it's one of several items currently on offer in the Next clearance so you might have to wade around the website to find the bargains best suited to your children's needs.
All I can tell you is that while Next clothing tends not to be particularly cheap, it is generally robust and hard-wearing, making it pretty good value for money. And I speak as the mother of boys who tend to go straight through the knees of any and every pair of trousers they wear.
My kids also have gilets and I've found them to be the perfect compromise to the where's-your-coat war that we seem to have every time we need to leave the house. Perfect for adding warmth without overheating or feeling too bundled up.