Howe, of Castle Road, Chatham, and Ezeorji, of Porters Avenue, Dagenham, have pleaded guilty to neglect.
They were told by the court their actions showed “total disregard for a person’s life”.
Magistrates heard Ms McMullen is deemed a very vulnerable adult.
She needs two-to-one care 24 hours a day as she is in danger of choking on food so she must be supervised at all times.
The court was told officers had to smash a window to free Ms McMullen because they were so concerned about her welfare.She was immediately given water and drank it thirstily before being taken to hospital by ambulance to be checked over.
Ezeorji and Howe returned to the vehicle at about 4pm, two-and-a-half hours after they had abandoned her inside.
Police were still on the scene and arrested the pair on suspicion of neglect.
Both were later charged and pleaded guilty at Medway Magistrates’ Court.
They returned to the same court for sentencing.The court was told the pair had admitted their actions fell below what is required of them and said they did go to check on her in the car, but left her there again and just forgot about the time.
Magistrates decided their sentencing powers were insufficient and sent the case to Maidstone Crown Court to be dealt with.