Many people think so. A few object. How can this be answered?
If a male child, say age 7, thinks he is a girl, only wears "girl" clothes, keeps his hair long and neat, likes to pay attention to clothes matching, identifies on the toy aisles liking the "girl" aisle, does not like being forced to assume boy roles, or friends, or toys, is this male child a girl? He presents his/herself as a girl, thinks like we expect girls to think, and other children identify him/her as a girl, is that enough? Again, many think so, yet a few object vehemently.
Here is a recent case: http://www.nydailynews.com/news/national/transgender-boy-attempt-join-girl-scouts-initially-rejected-boy-parts-article-1.968179