What do you suggest if my doctor has given methylcobalamin 1500mcg to my 7 yrs old child for 1 month. is it a high/toxic dose?

Probably not toxic: This is a vitamin B12 analog and, since it is water soluble and therefore easily cleared from the body, is probably not toxic. Before stopping the vitamin, it is important to know why it was prescribed. This dose is only slightly higher than the NIH's recommended daily allowance, but you should remember that he is likely getting B12 from dietary sources as well.