Hi what can i do on my exercise 11 or 12 year old girl

Almost anything: Playing a sport, whether organized or not, is usually sufficient as long as it is done 5 to 7 times a week. If a child is not "athletic" or just not interested than regular walking or bike riding is sufficient but needs to be continuously for at least 30 min and as frequently as playing a sport. Good nutrition is important. This means drinking mainly water and limiting sugar/carbs.