But do you really* want your child to learn to "win a fight" or to "fight"? To what degree? Any fight whatsoever? Doing so would require teaching things (s)he does not fully understand and are emotionally unprepared for, e.g., maiming or killing someone. [OTOH if you want to teach that to a child, then teach him how to be a doctor b/c doctors know how the human body works better than almost anyone else and how best to turn it off.]
Instead set other goals: self-confidence, pride, athletic skill and endurance. I would first explain the role MA plays and constantly emphasize avoidance of hostile situations. IMO teaching anyone (including children) good evasion/escape is more useful than MA and more fun.