Rear Drivers side door wont open from inside

Hi, looking for a bit of advice on this one, this morning my 10 year old Grandson tried to get out of the car but the handle inside would not work, I assumed that the child lock was on so I just got out and opened the door from the outside, on closer inspection, the child lock is not on, I turned it on and off again to make sure, but the door will not open from the inside, works fine from the outside and it locks and unlocks normally... any sugesstions??

Thanks in advance.