Becoming Religious Includes Your Pets
One of the ways you can tell if a family was once secular is if they have a dog. It is extremely rare to find a dog in a frum-from-birth home. When Mom and Dad decide that they want more Torah in their lives and embark on a mitzvah-observant lifestyle, giving away the family dog or cat is not an option. The kids are pretty attached to the family pet, and giving away their precious friend is something that could make the adjustment to a new lifestyle painfully difficult.
There are actually quite a few halachic considerations for your pet too, and in some ways, having animals give you the opportunity to do more mitzvot.