Two boys from two different worlds have what the other needs to live. The price looks just right for the exchange… except, not everyone is keen on having them alive.

This vaguely sounds like a logline, but it isn’t one.

“Two boys”: so it is a dual protagonist movie? Unless you have some experience (which – with respect – the logline doesn’t suggest), I would recommend to stick to one main character. See here why: http://thestorydepartment.com/stick-to-one-hero

“What the other needs to live” is awfully vague. We can’t imagine anything exciting for this movie. Be clear about what to expect, so the reader has a reason to want to see it.

“Not everyone is keen…”: this suggests an antagonist but it is so much more interesting if we know the identity and motivations of the antagonist.

The logline now reads like it is saying “I have a really exciting story for you, but I’m not going to tell you what it is about.” This never works.

Back to the drawing board!