A Bronx father who drowned his 5-year-old son and poisoned his 6-year-old daughter Wednesday was charged with murder, police said last night.

Leonardo Espinal, 47, was being treated at Bronx Lebanon Hospital because he had ingested rat poison in a failed bid to kill himself, but was transferred to the 46th Precinct station house to be charged, police sources said.

The boy was found in a tub; his sister survived.