A deranged individual is threatening to kill the 5-year old girl who plays Charlie Duncan on Disney's "Good Luck Charlie" ... and TMZ has learned cops are taking it very seriously.
According to police docs obtained by TMZ ... Mia Talerico began receiving threatening messages last month on her Instagram -- including one reading, "Die Mia, F**king Die in hell! Kill yourself, you deserve to die."
The suspect then sent a picture of Mia's head with a bloody fist covering it ... with this message, "Yes, kill you stupid bitch."
Mia's mother contacted Disney security ... LAPD's Threat Management Unit got involved ... and now cops are making a full court press to track down the suspect.
What kind of sick person does that?