America may well go after you and we have a large military to do it with. most often a simple diplomatic message will shut you down - most countries have their own child porn laws, and the exceptions (if any) are going to face problems as this is something the us takes seriously.

You picked a bad example - there are many US crimes that you could get away with if done elsewhere within the local laws, it generally isn't seen as worth bothering with when done elsewhere if the other country doesn't care.