The boy, 2 months old, sustained a head injury in a traffic accident Saturday, and was dead when the St. Petersburg family arrived at the church, RIA Novosti reported Monday.
Investigators said his parents brought him to the church, because "otherwise he would be denied the kingdom of heaven," the Russian news agency cited his parents as saying.
The unidentified parents, in their 40s, were being investigated for "failure to assist a person in danger," RIA Novosti said.
"This is superstition, not religion," an unidentified spokesman for the St. Petersburg Orthodox Church said. "They should have gone to the hospital."