Does climbing trees count?
I lived next to Golden Gate Park when I was in the 4th grade, and I used to spend my free time climbing the highest trees I could find. By the time I was in the 6th grade, I could climb trees better than Tarzan and had enough strength to do legless rope climbs with about 30 pounds tied around my waist.
I was the strongest kid in my class from then on out.
By the 8th grade I was lifting weights avidly and continued throughout high school and college.
While I was in the Corps, I was the Obstical Course champ for Dog and Pony Shows for visiting US Congressmen and had no problem beating anyone who they put me up against. Once I was asked how come I was so good and I simply said, "Trees, sir!". (We weren't allowed to speak to Congressmen unless they directed a specific question at us individually. And then we had to answer concisely and with few words as possible ... with a "Sir!" followed at the end.)
So, yea, I think lifting or any other strength building exercise is of great value for 13 / 14 year old kids. But even more important is the fact that they are committed to doing something athletic to improve themselves - be it lifting, or football or any other strength and character building endeavor.
My sole regret is that I never climbed to the top of a Redwood tree which I've always wanted to do as a kid. Those initial branches were just too darn high to reach and the trunks were to darn large to shinny up. I tried but never was successful.
And now I couldn't do it even if you gave me a ladder, so accomplish your dreams while you're able to get to reach your goal. If you wait, it'll never happen.
And encourage your sons and daughters to do the same.
One last comment here - when my nephew was three, he used to stand on my brother in law's shoulders while they rode a unicycle up and down the block, so I bought him a couple of month's membership in a local Gymnastics studio. 20 years or so later he was one of the lead performers for Cirque de Soleil's Mystere in Las Vegas doing backflips off one pole onto another and now he's involved in some of Hollywood's major movie productions. All this because he rode on top of his dad's shoulder on a unicycle when he was three and got some encouragement from his Uncle Stunt.
My point here is that we should all encourage our kids or even the neighbor's kids when kids do something they enjoy that will help them do better in their adult years.
Good job, Power and thanks for starting this great post.