The FIRST Lego League (FLL) is organized by FIRST. I’m not familiar with the FLL, but I know the FIRST family of competitions. Our school district has all three levels, and I help with the FRC.
Website is located at http://www.usfirst.org/roboticsprograms/fll
Learn how to start a team at http://www.firstlegoleague.org/challenge/startateam
Some costs https://gofll.usfirst.org/pages/product_description_and_pricing
The whole FIRST organization has a large group of volunteers to help people like you get started. Mostly to guide you through everything, but also show you fund-raising methods and sponsorships. The Senior Mentors is your best contact, and have local people in each state http://www.usfirst.org/community/volunteers/first-senior-mentor-program.
There are also the FLL Partner for each area at http://www.usfirst.org/regional-contacts
There is also an FLL forum http://forums.usfirst.org/forumdisplay.php?f=24
Locate local teams and events http://www.usfirst.org/whatsgoingon
The FLL season starts with a new competition “Kickoff” September. “Build Season” is October and November, and Tournaments are November into February. Registration for the fall begins in May. Now is a good time to do all the groundwork – school contacts and space to work, learning how to use the kit, and maybe trying out previous years challenges. If there is a “technology” teacher in the high school he/she may be a good inside source of school connections, and maybe supply students in the fall to help after school.
It is tough getting parents to help, especially directly after school. If you treat it more as adults guiding the students and keep them focused and the work fun, and less as teachers doing the work, that helps. Ask the parents to come in and see what their children are doing and let them show off their creations. Say you really need a second adult to be around. Most adults are afraid of breaking something or not knowing what to do. The kids are supposed to know what to do (with your help); the other adults are just to keep them focused.
There are two other levels of FIRST robot competition. FIRST Tech Challenge (FTC), for upper middle school into high school grades have larger robots but are still mostly kit-built, and FIRST Robotics Competition (FRC) for high school, where you get into more “real world” engineering and construction, and get to build large robots. The reason I mention FTC and FRC is that those teams are encouraged to support younger teams and (if local) come help with the technical issues. After all, they may have originally started in FLL! The locate local teams link can help you find them. (For some reason, the FLL teams aren’t listed.)
The FTC has a similar season as FLL. The FRC is now in the middle of their build season, and will start competitions each weekend in March at different locations all over the US and the world. The enthusiasm at a FRC competition is intense, a mix of sports and science fair with much geek-level socializing, each with around 50 high schools attending. It is free to the public to attend, and you’re allowed to visit the pit area and see the robots up close. Ask questions with teams in your area and you may find a team to help you. Good luck!