Removing the Door Panel & Fixing the Rear Window Child Lock
on an Audi A4 1.8 L (B6 2003)
Some other sites have good documentation on removing the panel as well:
Audizine.com: DIY Window Regulator & Motor Replacement
Audiworld: C5 Rear Window Lockout Switch Repair (diff. model)
Removing the interior door panel
Carefully pry up cover plate under door pull arm rest from below to reveal 2 screws. Pry up the long cover trim located above the door handle starting from the front edge then slide out the other end as shown to reveal 4 more screws. Last door panel screw is at the bottom.
(driver's side shown, passenger side has only one screw under door pull)
7 screws total, but 8 snap clips shown below still hold the panel. Start by prying away the bottom at one of the corners with something relatively soft between the panel and the black weather stripping. Some of the clips will likely break. Two or three of mine did partially. I still re-used them. If you need to replace any the part number is 8E0868243.
Child Window Lock Button:
You can get a new set of buttons for ~$80 online. I fixed mine, though it's hard to say how long the repair will last. I removed the button. Another write up for a C5 has pictures that may help: Audiworld: elec186.shtml (though that button is different). Remove the 11 door pull screws. Remove the mirror button plug and the window button panel plug. Work the button panel out by slipping a small screwdriver near the four clips.
Removing the spring wont fix this one. I found the broken fragment outlined below in the white grease where a wire tracks to hold and release the button. I started with a small dab of thick Loctite super glue for plastic. Then I used a drop of very thin modelers super glue to wick into the corners and crevices. Surprisingly it is holding. I plan to leave the windows unlocked and not mess with the button.
I also managed to get the door pull nice and clean using some citrus hand cleaner (the kind WITHOUT pumice). Be careful or you'll remove the finish.