invaded

What is it that invades children over Christmas vacation? I swear these are not my kids. One minute they are playing happily together and the next they are at each others throats. Swear something invades them at the beginning of any vacation and chases the sweetness right out the door. Conspiracy against parents and sanity. Scientists testing the adults of America... what exactly is the breaking point? And where in the meantime do they store our real children at? Anyone know?