Each FCFL League may use slightly different Modified Tackle rules, check with your specific league to get the exact details, Copied below is some information from USA Football on what they call Rookie Limited Contact Football. I also attached a link to the Limited Contact page on the USA Football website. It explains both versions of Limited Contact Football and talks about the benefits for this new option to get kids ready for Full Contact Football.
Rookie Limited Contact introduces athletes to contact slowly, focusing on proper skill development. Fewer players and a smaller field ensure the game isn't overwhelming but is still lots of fun. This Game Type slowly adds contact and builds great skills.
BRIDGE FROM FLAG TO TACKLE
Stay on two feet while learning the finer points of blocking, defeating blocks and tackling through Limited Contact. A progression of skills and reduction in contact are centerpieces of this path to play.