On my driver's side, the back car door will open from the inside, but not the outside.
Generally, the outer door handle itself is the issue. You will want to get this repaired as soon as possible; if someone hits the child lock switch, you will not be able to open the door at all. You may want to enlist the help of a mechanic, like one from YourMechanic, who has the tools and knowledge to repair the outer door handle.
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