Both had suffered "blunt force" head injuries. A county district attorney says the babies either were hit with something or were hit into something.
A police complaint says the babies were found Sunday after officers were called by the twins' mother, who had gone to pick up the children after work. It says the infants had been at the home since Friday.
A defense attorney for Yates says his client takes "behavioral medication" and may not be competent to deal with the legal system without it. The lawyer says he's not confident in Yates's ability "to make the right decisions."