Four toddlers of a Houston family tested positive for cocaine, including twin 11-month-old boys, after police said nurses became suspicious when one of the twins showed little pain despite a fractured arm.

Parents Emanuel Jones, 43, and Tammy Lynn Melton, 25, have been charged on felony counts of child injury and remain in jail. Both tested positive for cocaine and antidepressants and were arrested late Wednesday, police said.

Authorities said they are unsure how the children, including a 2-year-old girl and a 1-year-old boy, ingested the drug. In all, the two cared for eight children, including twin newborn girls.

"Either the parents are smoking cocaine around them or they are sharing it with them," Catheryn Gardner-Sanders, a Houston police investigator, said in Thursday's online editions of the Houston Chronicle.

All of the children have been removed from the home and placed in foster care, authorities said.

The parents were arrested one week after taking one of their twin boys to the hospital with a fractured wrist. Nurses called police when the infant wasn't "showing the pain reaction a child should show," Gardner-Sanders said.

Jones, Melton and the eight children lived in a bug-infested, one-bedroom apartment in northwest Houston, police said. An invalid great-grandmother also lived with the family.

Jones and Melton both remained in Harris County Jail late Thursday on charges of injury to a child by omission. Bail was set at $5,000 each, according to the Web site of the Harris County Sheriff's Office.

It was not immediately clear Thursday night if Jones and Melton had attorneys.