What is the safest way to lose weight for a tween?

Burn calories. Swim, bicycle, abdominal crunches, find 300 calories a day you don;t need to eat e.g. Bread. If you eat meat, make it lean, take off the skin of chicken, no fried food, eat more fish and seafood, eat green and white veggies cooked with garlic and oil. Rice and beans(lentils and rice) are good sources of complex carbs.