Here are the pants (or longies) I made for S a year or more ago. They're wool so once they are properly lanolized (coated with lanolin), then they act as a great breathable, water-resistant, natural diaper cover. He's been wearing them since I made them and as you can see in the picture above, they're a bit long on him there, but since the stockinette bottoms roll up a bit, they worked on him then and they still fit him now.
They're actually really lovely to knit. The pattern is so easy I don't even have to look at my hands, which makes it a great project for my Stitch & Chat group or watching TV. And they're so cute. I modified the pattern slightly, increasing a stitch down the pant legs every 5 or 6 rows which added an extra inch or so to the leg width to make them a little wider legged. D asked how many balls of yarn it would take to make a pair big enough for him. When asked he said he didn't want a pair, but I don't believe him.
Here are the wool shorties I made for Simon. These were made before the wool pants above. They were great for summer (last summer, but I can still squeeze him into them) They're cargo shorts, a little tighter than I'd like, maybe, but I really like them anyway.