If it helps you in your search, sometimes they're called cowls or circle scarves. I like to knit these for myself. There's no ends flapping in the breeze and I can pull them up over my face if wind and cold snow blow. It's basically a tube that's not closed on top. You can use any hat pattern for the correct yarn, needle size, and number of cast on stitches. For the adult size, 12 inches high in a k1,p1 or k2,p2 rib is good. The rib keeps it snug around the face so it won't fall down. You can also knit a one inch rib at the beginning and end of the scarf and the middle part in stockinette if you wish. Knit in stockinette, this is great for Fair Isle work. You'll have to do a little measuring to get the right height for kids. Keep in mind that it should cover the neck and up over the nose to the eyes when extended up for bad weather.
I love mine. It's come in handy numerous times when I'm waiting for a bus after work out in the open with bitter cold winds. I've found that wool works the best. It easily tucks into a corner of my bag so I can pull it out whenever I need it. The nice thing about these is that it uses very little yarn, a lot less than a long scarf.