did you check to see if you can take apart the housing? because the rear seat belts (which i am guessing youre talking about because of your kids being buckled in) are normaly in the kid zone, they usually get abused by kids. you know how the kids spill EVERYTHING in your car, soda candy, chocolate, sand, mud from water mixin with dirt when they spill water, etc., the seat belts often get jammed up. try takin them apart and clean them. if you cant, try spraying WD-40 in them and work em in and out to get the internals working freely again. make sure they still lock when you yank on them real quick. in the dealership we see this very often but we usually replace them instead of take em apart. we do spray WD-40 in them to try and save the customer money but we cant sin every time. good luck