A California man has confessed to killing his two little children with a spearfishing gun in Mexico because they inherited “serpent DNA” from his wife and “were going to grow into monsters.”

Matthew Taylor Coleman, whose act was influenced by “QAnon and Illuminati conspiracy theories” made the statements to federal investigators after being arrested at the border in the wake of Monday’s double filicide, court documents show.

The 40-year-old was reported missing by his wife on August 7 after he left his Santa Barbara home with his 10-month-old daughter and 2-year-old son without a car seat for the infant and took them to Rosarito.

He allegedly shot them dead through their chests with the spear gun and was arrested by Customs and Border Patrol as he tried to re-enter the US alone two days later, an FBI affidavit said.

The border cops “observed what appeared to be blood” on paperwork in his vehicle, and Mexican police found the bodies of young victims matching the description of Coleman’s kids in a ditch, according to the document.

The suspect waived his Miranda rights and told the feds “he believed his children were going to grow into monsters so he had to kill them,” according to the affidavit.

He was charged with the foreign murder of US nationals and was slated to appear in an LA court Wednesday.