Repairing the watches:
OK, so I decided the crooked screen wasn't really too noticeable, so I am going to leave it alone. I am giving the 4 good working watches to the kids, and I want to make sure the warranty is good for them in case anything stops working.
As for the 5th watch, the one with the loose screen, I decided to open it up and void the warranty in an effort to fix it. It was easier than I thought it would be.
First, slide out one of the pins in the wristband as if you were going to shorten the band. This will get the band out of the way and make it easier to work on. Using a jeweler's screwdriver, remove the 4 screws on the back of the watch and lift off the backplate.
Inside, the entire system is held in place by only two small screws, and they were very loose. I think I know why. The watch was even more glitchy with the screws tightened down. It seems the chip was not manufactured to a good enough tolerance, and there was actually the edge of a circuit printed underneath the area that the screw contacted to hold the chip in place. With the screw tightened down, the case now becomes part of the circuit, and you get problems when you insert either the headphones or the USB adapter, because the jack goes in through the metal case and creates a short in the circuit somewhere.
I fixed this by cutting a small rectangle out of the plastic protector that was covering the face of the watch to protect it during shipping. The size of the rectangle I cut was small enough that folding it in half made it just a little bigger than the head of the screw. I used a tiny jeweler's screwdriver to poke a hole in the folded plastic, and used it as a washer to insulate it from the circuit. I did this to both screws.
While I had the screws out, I also cut some strips of the same plastic to cover the length and height of the inside part of the watch housing that contacts the top and bottom of the circuit. This insulates the circuit in case any of it was printed too close to the top of the chip, and it protects the LCD's delicate ribbon cable from rubbing on the metal (on the bottom, the strip of plastic is meant to be slid between the ribbon and the metal housing).
You have to actually lift the circuit out of the housing just a little bit to get the plastic strips where they need to be. Be very careful not to get any dust inside the watch, and if you actually remove the circuit all the way from the houseing, make sure not to get a fingerprint on the screen or the inside of the watch housing's glass window.
Once you get the plastic insulation strips in the right place (it could take a couple tries), put the two newly insulated screws back into the watch, and tighten them down to secure the screen.
After making these mods, the watch that was shipped to me with a loose and glitchy display screen works perfectly. The only problem is that I have just voided the warranty on this watch, so I guess time will tell how reliable it is.