A good friend of my was consulting me on his family's quest to develop some healthy lifestyle changes that would impact his children's lives and create robust positive attitudes and strength for a lifetime. 

As we discussed the obvious whole foods, fruits, and vegetables and cutting back on the purchase of processed foods, we soon turned to discuss workouts and exercise that might be appropriate for his children.  His thirteen year old son has a particular interest in weight lifting.  From MayoClinic.com;

Experts now realize that with good technique and the right amount of resistance, young athletes can avoid growth plate injuries. Strengthening exercises, with proper training and supervision, provide many benefits to a young athlete.

Supervised strength training that emphasizes proper technique:

• Increases your child's muscle strength and endurance
• Protects your child's muscles and joints from injury
• Helps improve performance in a particular sport

Your child may gain other health benefits from strength training, too. These include:

• Better heart and lung function
• A healthy body composition
• Stronger bones
• Lower blood cholesterol levels
• A good fitness habit that lasts a lifetime

Some studies suggest that improved self-esteem and a decreased chance of depression also are upshots of strength training.

Older preteens benefit the most from strength training.  Most importantly, be certain your child receives proper instruction to ensure safety, effectiveness, and develop a program to create a balanced musculature that will avoid injuries, overload, and burnout. 

Fitness is contagious, glad to hear you are a Dad leading by example.