I've never known a kid to not appreciate a bright coloured cardigan, and if you've been looking to get into knitting this is a great pattern to start with. It's easy knit, just stocking stitch and garter stitch, the stripes are optional, and it's a nice drop shoulder sleeve. Done in chunky yarn, it's going to knit up quick too.
This has been written in King Cole Big Value Chunky, a standard workhorse yarn with a great price point. If you're looking for something a bit fancier, why not try the Timeless Chunky? 10% alpaca wool makes it super soft and warm. You'll need 5.5mm and 6mm needles.