Child locks are only on the rear doors.
Yes, you'll have to pull the door panel to see what's going on.
The most common problem with the door handles is the actual handle itself cracking and breaking off. Sounds like your handle is intact.
Inside the door panel, the handle is attached to the control arms (metal rods that go from the handle to the latch) with two little plastic clips. There's one arm for opening the door and one for locking it. Could be that the control arm popped out of its clip, but not real likely because of the way they attach. Could be that the clip cracked/broke. If it just popped out, you'd just have to pop it back in. If the clip broke, I believe you'd have to replace the entire door handle. If you need a new handle, eBay is your friend.
I've never examined the other end of the control arms where they attach to the latch, so I can't tell you about that end.
The little white clips near the pliers are the plastic clips I'm talking about. The metal rods are the control arms. The one on the bottom is the one to open the door.