Yah El Bresko is onto something because 10 minutes of BJJ class is devoted to warming up, stretching, then another 10 minutes for instructions and forty minutes of rolling around dripping in sweat and battling for your life. El Bresko was able to learn and go through all the motions already.
BUT it's extremely important to get the technique down. That can only be taught by a certified instructor with proper credentials. Tons of Black Belts out there, but ya should dig into their backgrounds. Reason I say this, it sounds like you want to take your kids far in this sport being a competitive athlete yourself. You can't stick em in a Karate gym that changed into an MMA gym. Any Gracies, Machado, 10th planet, Drysdale, Marcello Garcia affiliates, or any top camp will have a BJJ program to fast track your kids from the ground up. There's no coincidence that any fighter from those camps are top notch when it comes to the art of Brazillian Jiu Jitsu.
Basically if I had my choice I would pay any amount to train under Rickson Gracie followed by the original Royce. I've checked out a Marcello Garcia seminar, but that's later on for your kids. Great to see you're such a supportive father!
Marcus Aurelius: Tell me again, Maximus, why are we here?
Maximus: For the glory of the Empire, sire.
Baked, not fried... the healthy choice.