Personally, I would be very wary of using any form of chelation therapy unless there really is evidence of heavy metal poisoning. However, using methylcobalamin would probably be safer than using EDTA, since methylcobalamin is simply vitamin B12 (otherwise known as cobalamin) with a methyl group (-CH3) attached. EDTA on the other hand, is a powerful chelating agent which is commonly used in the laboratory to chelate a variety of different metal cations (positively charged ions).
I have no doubt that differences in the uptake, distribution and storage of metal ions can account for a number of diseases or conditions. Metal ions are intrinsic to the structure and function of numerous proteins, and proteins perform a multitude of tasks within a living organisms - structural (skin, hair), messengers (hormones) and virtually anything else you can think of. Not surprising then, that if metalloproteins cannot adopt precisely the right structure (perhaps through lack or excess of a particular element) then they will not function correctly.
However, the human body appears to be very good at ridding itself of toxins and making sure there is enough of the good stuff, given half a chance. I think food cravings are not confined to pregnancy, but instead are a general mechanism for regulating our dietary requirements. Similarly, I don't think loss of appetite is necessarily a bad thing. I'm sure everyone has noticed that as the weather is getting warmer, you might be content with a salad rather than the steak and kidney pudding of a few months ago!
Although I don't have any children, I do suspect that I have AS, so here is my personal opinion. What has really helped me is being able to eat what I want, when I want, without anyone trying to pressure me. Usually I will have 3 meals a day like everybody else, but then sometimes I'm just not hungry or really fancy pizza for breakfast, so that's exactly what I'll do. Of course I can see that could be quite a difficult arrangement to have with a child in a family setting. The other thing that has been a real help is yoga and meditation. Of course, this may also be a difficult thing to involve a child in, and I would definitely not recommend some of the practices for anyone under 18. Aside from the asanas (positions) I have been doing some kriyas (cleansing practices) which are designed to rid toxins from the system and restore a good flow of energy. These involve purging the nasal passages, stomach, and fasting. Sounds like bunk and it's not overly pleasant but you feel great afterwards! Also, saunas and especially steam baths are great, as long as it's quite dark and there's nobody else in there with me...