Thunderbirds/WMG

Brains is a time traveler from an even more distant future.
It is known that International Rescue's technology is "years ahead of its time," far in advance of the state-of-the-art in both the military and private industry.

On-screen, the justification for International Rescue's secrecy is glossed-over.

Logical conclusion: Brains got his advanced technology from the future, and the secrecy is an attempt to avoid damaging the timeline too badly.
 * My guess is he's a Time Lord.

Jeff Tracy's sons were all made artificially.
Using state-of-the-art cloning technology and the finest genetic codes known to man (including his own), the brothers five were born. Each of them are at the peak of human physical and mental abilities.
 * Oh... So would that explain why their hair stays so perfect?
 * Yep!
 * According to the official canon, the Tracys did have a mother, but she died.
 * What's this "official canon" business?
 * The Complete Thunderbirds Story states that she died in an avalanche whilst on a ski trip, an accident that also claimed the life of Grant Tracy, Jeff's dad.
 * Hey, just because they had a mother doesn't mean she's the sole biological mother. Perhaps she was able to act as a mother before that accident. (it's an insult to consider adoptive mothers as less than real.) Or perhaps even state-of-the-art cloning tech hasn't come up with a better incubator than a living human female.

Thunderbirds occurs after a population-devastating disaster.
In wide shots of roads or cities, there are few cars in use, and no one is simply walking around. In interior shots, there are rarely more than a dozen or so people in a single room. Over the course of a full episode, we probably see only about 20 people.
 * As an extension of the above, the reduced population has resulted in a technologically advanced world with virtually no scarcity of fuel or resources.

Jeff Tracy had a wife.
Her name was Lucinda/Lucille, and she endured the birth of the Tracy brothers until she died giving birth to Alan.
 * Or through a car crash.
 * Or in an avalanche during a ski trip.
 * Or through childbirth during an avalanche in a car!!! Hey, it could happen!

Thunderbirds are NOT go!
The whole thing was a mere super-dream of Jeff Tracy, thought of during a coma.
 * Or Was It a Dream?

Fox Kids is right -- the whole show does take place in the Thunder-World.
You remember, the goofy teenagers watching over the re-dubbed Thunderbirds guys? Turns out they weren't that far off the mark.
 * Oh God, not "The Hack Masters"... Anyone but those teenagers!
 * That's what they wanted you to think. Two uber-pesky "Turbo-Charged" teenagers are far more relatable than 40-year-old Government scientists.
 * You mean... it's real?!
 * When us normal folks go into outer space, I call dibs on the extraterrestrial puppet hunk!

Thunderbirds are real people, not just silly puppets!
The show was made as a secret tribute to these unsung heroes.
 * What do you mean, they're puppets? They've had shows on late night telly.
 * The thunderbirds are the ships, not the people.

Thunderbirds are go!
What? Someone had to say it!

International Rescue's secret base is Tracy Island.
Think about it, guys. IR has to be based somewhere, and the Tracys are known for being secretive. They're rich ex-astronauts. Who better to go into the rescue business?

Jeff Tracy would mastermind the operation, while his sons operate the Thunderbirds.

Think about it. It makes perfect sense!
 * What, those rich layabouts with no day jobs? Get real.
 * Yeah, I mean have you seen Tracy island? There's no way for Thunderbird 2 to land, with all those palm trees in the way.

There was a sixth Tracy son, Walter.

 * He died during a training accident (but not a Training Accident), possibly being ridiculously irresponsible with the original Thunder Bird 6. After his death, Jeff decreed Walt never existed, and his sons complied. This also explains his reticence in creating a "new" TB 6.

Alan Moore got the idea for Rorschach's costume from on Parker.

 * In The Man from Mi5, Parker is wearing an outfit just like Rorschach's, minus the mask. Look it up if you don't believe me.