There are many synonyms for the phrase "little boy's room" that can be used to refer to a bathroom specifically designated for young boys. Some common terms include "men's restroom," "boys' lavatory," "kids' bathroom," and "potty room." Depending on the context and audience, more playful and informal terms may be used, such as "the john," "the loo," "the throne room," or simply "the bathroom." It's important to keep in mind any potential cultural or regional variations in terminology, and to choose language that is respectful and appropriate for the audience and situation.