Blac Chyna investigated over alleged drug use over Dream Kardashian's safety

The L.A. County Dept. of Children and Family Services is concerned about the well-being of Blac Chyna and Rob Kardashian's baby ... so much so they've gone to court to make sure she's protected.
TMZ has learned the Dept. has gone to L.A. County Dependency Court so a judge can determine if Dream is safe.