This is different than leaving one of a few when going to a store though.
Apparently the grandmother had driven the 2 older kids so the mom only had the baby in the car.
Also, see this report directly from the person that found the baby.
http://www.nbcnewyork.com/news/local/Mom-Arrested-After-Leaving-Tot-in-Car-to-Go-Shopping-391820551.html?_osource=SocialFlowFB_NYBrandFirst of all, he said baby was in car 10 minutes not 40. Also at then end he describes how she said where's my baby in shock and confusion. Not as in,why did you guys take my baby out of the car?
In the APP he said: Eckel said Gruen came out of the store with two other children at about 1:20 p.m. asking where her baby was.
"She knew she left the baby in the car," Eckel said. "I felt like crying. After something like this happens, you act on it and think about it later."
Many people took this to mean she knew as in she intentionally left him. It more probably reads as - she walked outside and saw the scene (or realized inside) and suddenly remembered that she left her baby in there.