Just a quickie about thermal bridging and air sealing. I can explain it in way fewer words and terms and scientific-ness than what you find when you go looking for information on the web. Thermal bridging is when there is too much stuff that is not insulation in a section of exterior wall. This includes most traditionally framed houses. Especially near outside corners and around windows. In the cold of winter, the inside room surface of these areas stay much cooler than the surrounding room temperature and condensation occurs, then mold.
Improper air sealing is when your builder tells you your house needs to breathe and he's not talking about an air exchange system. Improper air sealing allows air to enter your house through tiny pathways through and near these moldy areas. The mold spores are then breathed in by your children.