Seatbelt for 2nd row center passenger will not retract on 2009 Toyota RAV4

One of the children my wife is a nanny for was amused by pulling out the seatbelt and letting it snap back into the roof of the car. Today, he pulled it out (not all the way), and it will no longer retract. Any suggestions on repair? How would I even begin to remove the headlining to get to the actual mechanism?

Asked by for the 2009 Toyota RAV4