The unidentified boy is the brother of Camden Johnson, 7 months, relatives said.
The infant was pronounced dead at Carolinas Medical Center Saturday after police found him unresponsive at home. He is also the son of Wendy Johnson, 33, who was charged with involuntary manslaughter and child abuse, WCNC-TV, Charlotte, reported Thursday.
Relatives said the older brother killed Camden "out of jealousy," noting Camden's mother was not at home at the time of the incident, and added the older boy confessed to police Monday, using a toy doll to illustrate how he dropped the infant on his head three times, WCNC-TV said.
Charlotte-Mecklenberg police announced Thursday an "11-year-old juvenile male" was charged in the death but did not comment on the suspect's relationship to the victim.