It doesn't need to be warm, just waterproof. The best I can fidn so far are the Clippasafe one (which I've got, it isn't properly waterproof, and is, in any case, too big) or the Wynnster fleece, which may do at a pinch as it has reinforced knees - the bit that's most likely to get soaked by a baby crawling in wet grass (not that I can find a local stockist). I can't find any actual waterproof smaller than 18m. Does anyone know of something suitable?