It's all to do with microbes. Having a family pet—such as a dog or cat—means your children have higher levels of two types of microbes that seem to have a protective effect against allergic diseases, such as asthma, and can even reduce their risk of becoming obese. Pet owners and their families have around twice the amount of the beneficial bacteria as people who don't have a pet.
Researchers from the University of Alberta aren't sure whether the microbes come from the pet's fur or paws, but they do know the microbes create early immunity.
The trouble is that the researchers aren't sure if there's a critical window of time when gut immunity and microbes co-develop, and so don't know when it's a good time to buy that family pet. However, higher levels of the microbes have been detected in babies when there's a family pet around the home.