Hello, Welcome to HealthcareMagic forum. Most of the supplements available are made from milk proteins and which may or may not react with the immune system of a child allergic to many foodstuffs. Remember that many children are allergic to tree nuts like almonds as commonly as milk or egg allergy is noticed. It would be best not to speculate about the weight of the child in such case. The best management is to have a regular assessment of the child by his pediatrician for documentation and evaluation of weight and height growth and nutritional assessment . Apart from multivitamin and protein supplements , the doctor can also detect possible iron and calcium deficiencies and start appropriate hematinics supplements for them in addition . Over the counter supplements are not very helpful and cannot exceed the benefits of a natural wholesome balanced diet Sometimes appetizers like cyproheptadine may increase appetite temporarily but it cannot cure the underlying problem nor correct any specefic deficiencies .. Hence your doctor might alternatively refer you to a nutritionist for the better management of his diet and allergy . So the next best step you can take is to get your child a reevaluation , growth monitoring done if needed get a personalized diet plan appart from nutritional supplements . Hope this information is helpful to you. Wishing you and your child good health. Regards So in your child