Recently there may be two endearments in China I think. One is “小姐姐”. It means the girls who are young. If you want to ask a young woman a question, then you can begin with “小姐姐”. And she will be very pleased to help you. The other is “小哥哥”. It is the same as “小姐姐”. It refers to the young boy.

“小男孩” isn’t commonly used in daily life. You may usually find it in a book or magazine or something else. It is a written language. Though it is not commonly used, you can use it anyway. It isn’t wrong. If you use the word to describe a boy, it means cute. But the age of the boy should be limited. Maybe before the junior high school. Once you use the word to a senior high school student or older, it may show contemptuous.

Hope these will be helpful to you.

Depends on who you want to address. If you’re talking to a little boy you would rather say 小弟弟. If you’d like to address your boyfriend then 小男孩 would sound really weird. Here are some more common terms: <a href="http://blog.tutorming.com/mandarin-chinese-learning-tips/chinese-terms-of-endearment" rel="noopener noreferrer" target="_blank">http://blog.tutorming.com/mandarin-chinese-learning-tips/chinese-terms-of-endearment</a>;