There are many situations where the courts will provide "protection" to people who are not perceived to be capable of exercising their rights in the usual manner. Such cases are often referred to as "wards of the court", and include not only children but also adults with diminished capabilities to understand court proceedings.

I imagine that people from uncontacted tribes would fall into the same category, due to their lack of experience with the courts. in practice, though, I also imagine that the courts would not be very interested in any appeals they make...

In any case, none of the above applies to monkeys.