My son is having trouble adjusting to the fact that it is no longer shorts and t-shirt weather. And every day when I tell him to get some trousers on, he reacts as though I'm suggesting he wear something as unreasonable and unbearable as a suit lined with razor blades. So I cut up an old pair of my maternity tracksuit bottoms in the hope of making him a warm pair of trousers that he wouldn't find too offensive.
Enlisting the help of Winifred Aldrich's Metric Pattern Cutting for Children's Wear, I drafted a simple trouser block for stretchy knit fabrics, got chopping, overlocking, appliquée-ing, hemming, reattaching the waistband (made smaller of course, and getting carried away I sewed it back to front... but whatever, at that point I couldn't be bothered to unpick it and start over, and maybe it's even safer to have the drawstring at the back anyways...?).
The result was a perfectly sweet pair of sweatpants for a very active little boy. Cosy enough to keep him warm, comfy enough for him to enjoy wearing them, and cute enough (the paw print on the bum!) for him to actually want to put them on in the first place. Success!