Garza was watching Caspian and three other children while the boy's father, Eric Steinmetz, ran a medical errand for his grandmother, authorities said.
The homicide and child-endangerment charges follow a lengthy grand jury investigation capped by an 18-page report on the child's death. A pathologist told the grand jury that the boy had bruises and scratches on his body that were probably caused by a struggle in the bathroom.
"We didn't want to file charges until we were comfortable that we could make our case," said Chief Deputy District Attorney Matthew Falk. "This is a serious case, and we wanted to make sure we made a thorough and complete investigation."
Garza told the Morning Call of Allentown last year that Caspian was playing in the bathtub while she made two 10-minute phone calls, and that she later found him floating face-down in about 10 inches of water. She also said that she tried to revive him through CPR, the paper reported.
Dr. Saralee Funke, a forensic pathologist, testified that the child had small nonfatal bruises and scrapes over most of his body, consistent with a hand applying pressure to the body, according to the grand jury report.
Funke concluded there was no medical explanation as to why Caspian would drown in the bathtub.
Garza was sent to the Lehigh County Prison without bail following an arraignment. It was not immediately clear if she had an attorney.
