Is it true that if we sleep with the window open at night that we will catch pneumonia?

There are 2 types of pneumonia (viral and bacterial) and neither is caused by cold air or dampness. That is a common misconception. As long as no one can possibly get into your child's room, including with a ladder, the child should be safe breathing the air. How comfortable the child will be is another question. Hang a thermometer in the room to make sure the child is not too cold at night thru morning for the child's comfort level.There is no benefit for breathing night air, but, no danger from breathing it. It can be a comfort thing though.