HI there,
My friends 9 month old daughter just had an operation for very bad, obviously late diagnosed, hip dysplacia (sp?) and will be in plaster for a few months.
Anyway, I've discovered (well, was told about) an online shop which sells legwarmer-like things, but made of sock material (80% cotton, 5% spandex, 15% polyester). They're not specifially for plastered legs, but should fit them as they're quite stretchy and accomodating.
Just thought I'd let you know if you're wanting something absolutely gorgeous to put on your little one's legs. Just google 'baby legs' with an Australia search.