What is a healthy weight range for an 11-year-old?

Well, it depends on your height to some extent, but anywhere around 35 kilograms. 35 kilograms is good if you're 140 centimetres tall, so if you're a little taller add some weight, and vice versa if you're shorter. If you'd really like to know, you can figure out your BMI (google it), and take a look at a BMI chart.