help locating child

i am trying to help locate a child that was in a state facility in jacksonville florida, his siblings were adopted however it is believed that he was not. i do know that he died Dec 1957, but do not know where, how etc. we are trying to piece the family history together as my boyfriend is one of the last living relatives...where do we start? his name was Nickolai Larsen. we believe he was 13 when he died. any direction or help is appreciated.