I even use quilting cottons for my boys for pants and shorts. Obviously those are more warm weather than cold, but they work great. Just expect that the knees will wear out faster than bottomweights like corduroy, etc., but this way they get more interesting pants and shorts than just solids. (They're so happy because I found a new Transformers print - the ones I made previously just tore out at the knees a few months ago, after 1-2 years of wearing/washing.)