The student who allegedly murdered his ex-teacher and their 4-year-old child was indicted for the brutal crime, prosecutors said Friday in Manhattan court.

Isaac Duran Infante, 23, was not in court for the brief appearance.

Prosecutors say that Infante strangled his former DeWitt Clinton High School science teacher, Felicia Barahona, 36, and their little boy, Miguel, Dec. 22.

He allegedly told investigators that Barahona had “ruined” his life and he could no longer afford child support because his new girlfriend was pregnant, sources told The Post.

Prosecutor Nicole Blumberg said Infante admitted taking a cord and, in front of Miguel, “wrapping it around his ex-girlfriend’s neck until she turned blue, and the life drained from her body.”

Minutes later, he took a cord into the bathroom, where Miguel was weeping for his mother, and strangled him, Blumberg said.

Infante began an affair with Barahona when he was a 17-year-old student, and she became pregnant.

Barahona was fired in 2013 after the school learned of the relationship, sources said.