Erm, hardly shocking. It has been established since at least the 80s that vitamin B12 is essential for brain development, and any number of large scale developmental studies have been carried out to that effect.There are no non-animal sources for vitamin B12. If you find any doctor of medicine who will recommend a vegan or vegetarian diet to either a breast feeding mother or to a child, then they ought to be struck off.

Simply Googling for "vitamin B12 brain development" will return you any number of papers on the subject, but most of them are behind their respective journal's paywalls unfortunately. However, the fact their abstracts include works like "cerebral atrophy" might give you some idea of their content.