Boy's Hooded Tank, knit in Rowan Classic Cotton Denim, is adorable, timely, and really cute. (They now recommend Belle Organic Aran.) The handwarmer pocket really makes it!
This sweater can be made in any number of yarns, making it versatile across the seasons. The original denim colored Cotton would be a great option for spring! And an alpaca blend would make a deliciously toasty sweater. Just remember to match the gauge on the labels when substituting yarns, and knit a swatch before tackling the whole garment to confirm your gauge is dead-on. I'll completely understand if you want to make several in different colors; if I were a kid this would quickly become my favorite sweater!