The latest was a child in Louisiana on Wednesday, who was the 11th death this year, compared to four at the same date last year, said Amy Artuso, program manager for the council.
The group had hoped that last year's low number of hot-car deaths -- 24 compared to an average of 37 since 1998 -- suggested that parents and caregivers were more cognizant of the danger, Artuso said.
"This year, it was quite a surprise to have that many deaths by this date," Artuso told CNN. "I guess we were optimistic because of last year."
Police this week arrested the father
of an 8-month-old baby who died of hyperthermia, or an elevated body temperature, in East Baton Rouge, even though the coroner had ruled the death an accident, CNN affiliate WBRZ-TV reported. The father was charged with negligent homicide.
The father, a baseball coach, told investigators that he was supposed to drop his daughter off at day care but instead forgot and drove to the school where he was running a baseball camp, WBRZ reported.
The tragedies tend to happen when a parent or caregiver has a change in routine -- possibly a different parent chauffeuring the child to day care, being especially sleep-deprived or focused on other duties, Artuso said.
"It does seem to be a distraction issue," she said. "We don't have anything scientific to back it up, but more deaths do seem to happen toward the end of the week."
Temperatures in Baton Rouge reached 93 degrees on Wednesday. Inside a car, it can reach 110 degrees in 10 minutes and 120 degrees in 20 minutes, WBRZ reported.
Studies show that the car temperature typically spikes in the first 20 minutes, Artuso said.
She advised parents and caregivers to place an object with the child they'll need when they leave the car. such as a cellphone or their left shoe.
"You aren't going to go too far while wearing only one shoe," she said.
Georgia dad facing charges in 2014 death of son
The hot-car issue got much national attention two years ago when a metro Atlanta father was indicted on murder charges after his 22-month-old son was left in a parked car.
Last month, a judge agreed to delay the trial of Justin Ross Harris
and move it to a different venue because of publicity.
The Harris case was one of 30 children who died in 2014 after being left in parked cars, Kate Carr, president and CEO of Safe Kids Worldwide, told CNN last year. At least 44 children died in 2013, she said.
"A car can heat up about 19 degrees in as little as 10 minutes, and we've seen heat stroke deaths recorded when the temperature is in the 60s," she said.
She recommended that all parents
create a reminder when traveling with their little ones.
"Put something in the back seat where a child seat is always located that you're going to need at your final destination, something you know you're going to look for, like your cell phone, your purse, a briefcase," Carr said. "This, in fact, can happen to anyone, and we've seen it happen to anyone."