It sounds as if the linkage to the external door handle has come adrift or broken. You need to remove the door card to examine inside the door to identify the exact problem.
It is a shame you didn't remove the door card before you allowed your friend to apply the child lock. Now the only way in is to cut through the door card which will be expensive. After you have fixed the linkage inside the door you will need a new door card to replace the one you'll have cut through.
ChicksFan, July 2014
