We live above diner where carbon monoxide leak was, duration unknown. been open 3 months. could my 11 week old son have brain/body damage from this?

CO level: The health hazards of CO exposure depend on the level of exposure. Blood testing is available to ensure that it is not an ongoing problem. A CO monitor is available for your home as one precaution. Keeping your home well ventilated helps to reduce the risk.

Some basics: The leak from a distant source is likely to dissipate before it reaches your dwelling. We all can tolerate low levels of CO in our blood & still function normally. As mentioned by others there are simple blood tests that can reveal the CO level of any exposed person. If the kid was feeding/playing/growing well over this period the chances of a true CO effect are minimal.