Doctors estimate the children, ages 2 to 7, drank about an ounce of the fluid late Thursday afternoon before realizing it tasted wrong, said Laura James, a pediatric pharmacologist and toxicologist at Arkansas Children's Hospital in Little Rock.
Only one child remained hospitalized Friday morning after blood samples showed "measurable levels" of methanol, a highly toxic alcohol that can induce comas and cause blindness, officials said.
"It was a bright blue product that, if you looked at it quickly and didn't look at the label, did look like Kool-Aid and had been put in the refrigerator by mistake," James told CBS News.
Julie Munsell, a spokeswoman for the state Department of Human Services, identified the day care operator as Carolyn Bynum in the town of Scott, about 15 miles east of Little Rock. Bynum declined to comment Friday.
Bynum had a state license to care for 10 children in her home and had no complaints or serious compliance issues in the past, Munsell said. Child welfare investigators planned to interview Bynum on Friday.
The children all were examined by doctors at the hospital and the day care provided a sample of the windshield wiper fluid for laboratory testing, James said.
The toxicologist warned that many antifreeze or windshield wiper solutions have bright colors, which children can mistake for fruit drinks.
"I think the take-home message is not to have these products in the kitchen or where you're doing any kind of food preparation," she said.