How can we encourage children to start recognizing (and rising above) category boundaries from a young age?

"All conventions are boundaries, waiting to be transcended." (Cloud Atlas)

Perhaps learning from a young age to reject absolutes, to break down boundaries and embrace complications, would dissolve racial discrimination, sexism, sexuality based violence, religious intolerance, and the other social stereotypes and personal limitations created by labels.

I think being able to recognize boxes is the first step to improving our ability to "think outside the box".