Is fortified soy milk ok as milk substitute for 3 year old boy?

Soy milk: Unless your child has a milk allergy or is lactose intolerant, I would use whole, pasteurized milk

Yes: Unless the child has intolerance to lactose or casein, dairy milk would still be a better choice as milk. Otherwise fortified soy milk should be OK as it contains most essential nutrients including calcium, which is important for their growth. Potential allergies to soy should be kept in mind when using the product.