One of the ways that adults can influence the outcome of gender stereotyping is to talk about the many ways people are the same and different.  My Princess Boy by Kilodavis introduces the themes of bullying and being different, based on the experiences of the author's four-year-old son.   Your child may not know of anyone like this character but the conversation you have about such children can help your child respond with respect and kindness in the future.  

And if you have a boy in your life who likes dressing up as a princess, this book offers a positive model of family acceptance and unconditional love. 

Interesting article about gender identity development: Gender Identity