Toxicological Profile For Manganese from the U.S. Department Of Health And Human Services, Public Health Service, Agency for Toxic Substances and Disease Registry.
https://www.atsdr.cdc.gov/toxprofiles/tp151.pdf
Page (6) Effects in children
Studies in children have suggested that extremely high levels of manganese exposure may produce undesirable effects on brain development, including changes in behavior and decreases in the ability to learn and remember. In some cases, these same manganese exposure levels have been suspected of causing severe symptoms of manganism disease (including difficulty with speech and walking). We do not know for certain that these changes were caused by manganese alone. We do not know if these changes are temporary or permanent. We do not know whether children are more sensitive than adults to the effects of manganese, but there is some indication from experiments in laboratory animals that they may be.