There are convincing studies of kids in Switzerland: some have strong immune systems (for example, they don't easily catch the flu) and some have weak immune systems (for example, they are allergic to a lot of things). The kids with the strong immunity were often located, when they were babies and toddlers (i.e. early in life) in the proximity of cows, on farms, where they breathed/absorbed floating particles in the air, they touched particles with their hands and then they did what kids do, etc.

Kids that were kept in hospital-like antiseptic environments in the cities, or away from farms, developed weak immune systems, had allergies all the time.

I think the same type of studies were duplicated in other areas of the world (like India) with similar results.

Now, we also know that living in unsanitary conditions (including molds) kills kids.

I think you and your wife offer a balanced environment to your child.

Molds are specially bad; if they are allowed to grow in grout that is kept moist and warm, like in some corners of the house where no man would think of cleaning the floor (not just you, Taffy - it's in the DNA of men not to carefully mop corners), then they will cause respiratory problems. Probably not your child's case but worth mentioning: mold can even kill when the baby or the old person has a weak immune system.