If both are observed doing so and only the black child is forced to leave, that child's rights have been violated. 14th Amendment.
[Where does the right to swim in a public pool come from?]
Permission to swim in the pool comes from the property owner. Disposition of property lies in the perview of the property owner.
The public holds the property rights to a public pool. The public facility may NOT violate the equal right of both black and white children to swim there.
"All Property, indeed, except the Savage's temporary Cabin, his Bow, his Matchcoat, and other little Acquisitions, absolutely necessary for his Subsistence, seems to me to be the Creature of public Convention. Hence the Public has the Right of Regulating Descents, and all other Conveyances of Property, and even of limiting the Quantity and the Uses of it." --Benjamin Franklin
This doesn't answer my initial question. Where do rights come from and how are they defined? From your posts and quotes it would seem you believe rights come from society. So, why didn't you just say so in the first place?
Now that we've established that you believe rights come from society how are said rights defined?