Either they will comply, or they won't. But their response will tell us pretty much everything we need to know their nature and intentions, won't it?
No. "They" could have millenia on their hands and readily comply, leaving behind whatever "treasures" the
primitives negotiators requested as proof of good faith. When they come back, you're back to square one.
I think the bottom line here is that it's pretty much impossible for a toddler to plan a viable defense against the adults' schemes.
And I don't even believe in UFOs...