Have a 2001 Lexus ES300 and since my parents bought it new, The back door will not open from the inside.

A rod connecting the inside handle to the locking mechanism has probably become detached. Usually they're just held in with plastic clips. To fix you'll have to remove the door panel, reach in through the door itself and reconnect it. Removing the door panel can be a little tricky, they can be held in with clips as well as screws. Screws may be hidden in/under the armrest and along the bottom of the panel. The clips have to be popped out, it can be done by hand but they do make panel removal tools as well (basically just a pry bar). As you remove the panel you'll have to reach behind it to disconnect the wiring harness (if it has one). Good luck.

What about safety child lock , every car have on back doors , is s small lever to be push on the other side !!!!