Living up to its name, the Saint Bernard is a calm, tolerant, and gentle dog breed. With that said, the Saint Bernard is a suitable choice for a family with kids. However, its sheer size is enough reason to make sure playtime or any interaction is well-supervised. We don't want the dog accidentally knocking over small kids.
When it comes to guarding, the Saint Bernard has no violent bone in its body so it may not be able to ward off thieves. It is also on the quieter side of the canine spectrum, so it is neither a watchdog nor a guard dog. When properly trained, it can be quick to let an owner know if someone is about. Also, its size is enough to scare away people not familiar with the breed.
The Saint Bernard is eager to please and, as such, is easy to train. However, do note that this working dog excels in dog sports including cart-pulling (drafting), weight-pulling, obedience trials, and tracking, so you might want to enrol this breed in dog training. Also, keep in mind that no matter how gentle a dog breed is based on its genetic makeup, a bored dog can develop undesirable habits and behaviours. Make sure that the Saint Bernard is given ample mental and physical exercises daily.
With its friendly nature, the Saint Bernard does not have a very high prey drive and will rarely show aggression to other dogs and small animals alike. However, when the mood strikes it, it may find small animals amusing to chase. so care should still be taken.