The point is that it doesn't matter WHY one is fasting. Fasting for a child who is growing changes the metabolism more dramatically than that of an adult, period. Doctors know this, and I know it from experience. It is far better to use another kind of cleansing method which will not affect the metabolism long-term (like raw foods, or the addition of fresh juices to the diet).
I will agree that short fasts are not harmful (up to 5 days max).
Here is a good word on cleansing diets I found on the web: (source cited below)
During a cleansing diet you will want to consume mainly whole grains, vegetables (preferably organic), fruits (again, preferably organic), pasta, rice, beans, and herbs. The more natural the diet is, the better. Consuming vegetables in a state as close to nature as possible is the healthiest for your body. When vegetables are cooked, they loose most of their nutritional value. Lightly steaming is a very good way to cook vegetables and still retain their nutritional value. It is also important to eat all organic foods if possible during a cleansing diet. Non-organic produce can contain extremely high levels of pesticides and chemicals. If you are unable to find organic produce, wash your fruits and vegetables thoroughly before eating them. Be sure to consume a wide variety of fruits and vegetables to ensure that you are getting enough of each of the eight essential amino acids. Soy products are an excellent source of vegetarian complete protein.
The second aspect of a cleansing diet is helping your body eliminate its toxin stores. The easiest way to accomplish this is by drinking water. Water is excellent at flushing out toxins and restoring health. You should drink at least a gallon of water a day (drink more if you are able). You can also drink natural herbal teas, natural lemonade (made without refined sugar), and other 100% juices. It is important to eliminate Sugar sodas, diet sodas, coffee, and teas that contain caffeine. Exercise is also an excellent way to help the body rid itself of toxins. When you sweat, toxins are excreted directly through your skin via your sweat glands. Sitting in a sauna for limited amounts of time can also have the same effect.
The length of time a cleansing diet is maintained is based on individual needs. A cleansing diet is unlike other traditional "diets" because it can be maintained indefinitely and become a life style choice. It can also be used periodically to help give your body a boost when you feel it is needed.
The benefits of detoxifying your body are both short and long term. Immediately after detoxifying you might notice increased mental awareness, more energy, more comfortable digestion of foods, and better absorption of nutrients, as well as an overall feeling of good health. Long-term benefits can include a reduced risk of cancer, reduced risk of environmental illnesses, and reduction of chronic illnesses.
Here's another marvelous cleansing diet site:
And another: (source site below)
Complementary Medicine - Tools & Quizzes
Naturopathic Cleansing Diet
by Jacqueline Young
Choose a time when you are relaxed and unworried.
Ideally follow the cleansing programme for 5-10 days.
Stop all tea, coffee, alcohol, sugar, refined carbohydrates, dairy produce and animal fats during the cleanse.
Don't eat fruit and vegetables together. Use organic produce whenever possible.
Muesli (unsweetened), oatmeal, live yoghurt, fresh fruits or prunes.
Lunch and dinner:
Choose from salads, wholegrain rice, baked potato, steamed or lightly boiled fresh vegetables, soya dishes, quorn, home-made soups and casseroles. If possible eat more at lunchtime and less in the evening.
Fresh, organic fruit or vegetable juices, herbal teas, rice, oat or soya milks. Also drink at least 6 glasses of good quality water daily.
Sunflower seeds, pumpkin seeds, nuts, vegetables (eg raw carrot or Celery stick) and fruit.
Drink an infusion of 2-3 young dandelion leaves daily, or take Milk Thistle (Silybum marianum), to stimulate liver function.
Take Golden rod (Solidago virgaurea) as a tea, tincture or supplement to stimulate the kidneys.
Use Slippery elm bark powder, psyllium husk powder, linseed oil and alfalfa to regulate and cleanse the intestines.
Echinacea (Echinacea purpurea angustifolia) stimulates the immune system.