inside v. outside isn't the whole question, but it does have a lot to do with the answer.
the issue would be whether the subject has a reasonable expectation of privacy in the place where the picture was taken. for instance, if they have a fenced-in backyard, and you took the picture over their fence, then you probably violated their expectation of privacy, even though they're outside. but usually, if you're outside, you are usually in a public place (on the street or park or wherever), and you can have no reasonable expectation of privacy in those places. on the same token, you can be inside, but if you're at a public party or something, you may not have a reasonable expectation of privacy (because it's a public function). or, a basketball game is technically inside. so inside/outside isn't necessarily dispositive.
i think the question is easily answered here because the picture is already in the public domain - being found on fark or wherever. now, the kid's dad could try to track down whoever posted the picture on the interwebs first, but he'd probably be disappointed to find that it was the kids themselves.
now, which one of y'all can i bill for this hour?...
ETA: magnolia hunter should definitely take and post some pictures, especially the kids chasing the mosquito truck. that's in the public street, and you'd probably be safe with those. you'd probably also make sixpackremembers. and as far as the stories go, if the statements are true, there's no defamation. also, even if you made up the stories, i doubt their dad could prove damages.