The phrase "in nappies" is commonly used to describe babies who are still wearing diapers. However, there are many synonyms that can be used in place of this phrase. Some alternatives include "wearing diapers," "diapered," "in diapers," "undergoing diaper training," "using baby pants," or "using disposable underwear." These synonyms can be used in a variety of situations, whether you are talking to parents with young children, discussing baby care products, or writing a health-related article. By using different words to describe the same thing, you can add variety and interest to your writing or conversation.