Oh shit, you've heard something...never mind anyone here who has kids that actually strength train, or those growing up who did farm labor.
Never mind all that - Fuck that. What's important here is that some random asshole who may or may not know the difference between a Clean, or Snatch, pass off his advice he probably heard from some other random asshole, tell you what's good or bad for kids.
Wow man, thats a little bit personal. But let me try to back up at least some of my opinions with facts.
The Mayo clinic agrees that kids can strength train, but the set the low age as 8
"As early as age 8... strength training can become a valuable part of an overall fitness plan"
Heres the link on that
http://www.mayoclinic.com/health/strength-training/HQ01010
The young man in question is only seven.
The American Association of Pediatrics also has some cavets for weight training.
"Preadolescents and adolescents should avoid competitive weight lifting, power lifting, body building, and maximal lifts until they reach physical and skeletal maturity"
Dr. Paul Stricker (a vanderbuilt professor) agrees, that any powerlift should not be done until after puberty.
http://www.vsm.vanderbilt.edu/documents/Stricker--STRENGTHTRAINING.pdf
Heres another interesting note. Pre-pubecent children, the gains made my strength training arn't due to muscle growth, its just do to muscle memory.
From the AAP: "In preadolescents, proper resistance training can enhance strength without concomitant muscle hypertrophy. Such gains in strength can be attributed to neuromuscular "learning," in which training increases the number of motor neurons that will fire with each muscle contraction. This mechanism helps explain strength gains from resistance training in populations with low androgen levels, including females and preadolescent males"
Strickers' article says the same thing. It is also worth noting that every one of these websites recomends consulting with a doctor before starting and strength training program on a child.
The bottom line: Kids can saftley strength train, however, they shouldn't do any powerlifts, and any gains they make are just muscle memory, not actually them getting stronger. So to me, the benefit of those over playing a sport or jsut messing around outside are minimal.