Children always should be supervised when lifting weights and instructed on proper form during weight lifting. Otherwise, yes, weight lifting is safe for children.
Exactly as you said: by lifting weights. Regardless of what type of weight-lifting program you are following, lifting weights will (and should; if not, increase the weight/reps) will increase muscle size and ultimately lead to a heavier weight.
This depends on the person and the kind of weight lifting you do. The short answer however is that lifting weights should help you to lose fat and gain muscle. If you are lifting heavily in order to gain muscle mass, you will gain weight. However, if you are lifting to get lean muscle, it should help to lose weight.
The National Osteoporosis Foundation recommends two different types of exercises: weight-bearing exercises and muscle strengthening exercises. Weight-bearing exercise means bearing your weight, working against gravity, such as walking. Muscle strengthening exercise means you're working against gravity while being still, such as weight lifting.
No it should not at all
push= using ur weight against gravity/forcing weight agaisnt gravity pull=using strength to pull with/against gravity (sorry my answer isn't that great and scientific!)
At the age of 21, a boy can start weight lifting. It is more advisable to start weight lifting at the right age. Because, some says if a boy starts weight lifting at an early age they not get tall. And their height will be the same as they start. I advice to take weight lifting, and make yourself fit, if your on the right age already.
There are many different types of weight lifting. There is Olympic Weight Lifting which includes Power Lifting, and then there is Strength Training and Body Building.
Assuming that each person is lifting equally the answer is 100 lbs each. The total weight 200, divided by 2. In reality it would depend on the center of gravity for the box, and also how evenly the weight of the box is distributed, plus also the height of the two lifters and the positions of their hands relative to the box's center of gravity.