Skeleton suits are often described as one of the earliest fashions to be specifically tailored for children, rather than being adult fashions sized down. Previously (and subsequently) young boys wore dresses until they were breeched, or put into trousers.
The passage describes how skeleton suits were a unique style that was specifically designed for children, rather than simply being smaller versions of adult clothes.  Previously and in the future, young boys would have worn dresses until they reached a certain age when they transitioned to wearing trousers.