Well, from what I understand about human pediatric development, it may be this poor child's organs were headed into failure--kidney, heart and eventually stroke. Generally, when organs fail, they dump proteins in to anywhere they can, then then the tissue becomes necrotic. That's why cancer or tumors are so bad, because that is what exactly they do to the body.

To, having too much protein in the blood, for a 3 month old is a very dangerous thing.

It sounds like they were unaware of his need generally. Babies just cry. They don't have distinguishable cries until 2-3 months of age. At the same time they don't make distinctions on who they are looking at until ~2 months of age--roughly the same time they try lifting their heads...

Most of the "mother books" somewhat describe these processes in terminology. But one never knows exactly what happens until she has her own baby... But generally, this his how it works.

The animals that are able to survive the first 6 months of life, will continue to reproduce. For humans it is the 1 year or so.

Even though they fed him, it was not enough nutrition. The child was probably nutient deficient if the mother kept her prenatal vegan lifestyle. So the child may have asymptomatic had birth defects.

These parents will have to live with their choices for the rest of their lives...