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, Saint Bernard have no violent bone in their body so they may not be able to ward off thieves. They are also on the quieter side of the canine spectrum, so they are neither watchdogs nor guard dogs. When properly trained, they can be quick to let an owner know if someone is about. Also, their 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, bored dogs can develop undesirable habits and behaviours. Make sure 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.