You’d need to ask a local attorney if you may be at risk of violating any state laws or local ordinances regarding indecent exposure. There is a possibility of that, but you really need to ask someone who knows your local law.
They have a right to use a trampoline or erect a play structure so long as that structure does not violate local zoning rules. The fact that they can see into your back yard does not mean that they are violating any right to privacy that you have, at least in a legal sense. They probably have no obligation to move that stuff just because you don't want to be seen nude in your back yard. Like it or not, the likely response to that problem is that if you don't want to be seen nude, don't go out in the yard nude.