Martial arts for kids

Jerry: Kramer, you're fighting children?! 
Kramer: We're all at the same skill level, Jerry. 
Jerry: He's nine years old! You don't need karate, you can just wring his neck!
- Seinfeld

Mat writes:

I'm looking for a Judo or Karate class for my kids locally. I'm in Crofton Park. They're young. My daughter is 6 and my boy is 4, 5 in September, so I appreciate they may be too small to start classes right now but when they're ready I'd like to get them involved. I was surprised at the lack of classes that come up on Google. Does anyone know of any locally that they could recommend?