I have never seen any guide lines on this topic and that is keeping the child cool in hot weather or vice versa. The tendency is in a lot of cases is to play safe and pile on outdoor clothing and/ or pram bedding whatever the weather. The very worst example I have ever seen, and this was on the hottest day of a scorching summer in Buxton. There's this mother extracting a howling newborn from it's pram. The pram piled high with assorted blankets and wraps topped off with a rain cover. The poor baby swathed in all kinds of woolies and shawls screaming it's head off. I stopped myself from offering any help or advice hoping that common sense would prevail. It was after this that I realised that toddlers are no better off. Winter coats and jumpers are a definate no no in hot weather.