The English mastiff was traditionally a warrior dog, trained to do battle with humans. Today mastiffs can be safely raised as domestic pets. Some mastiffs are used as guard dogs, but aggressive behavior is typically reserved for an appropriate setting. Mastiffs can now be said to be "man's best friend," and even get along well with children.
Behavior with Strangers
Certain mastiffs may be suspicious of strangers at first. Others will be friendly immediately. If your mastiff has been trained as a guard dog, it is likely that it will consider that its job for the rest of its life. A mastiff will not bite or harm a stranger under normal circumstances. If an unwanted stranger approaches to quickly, the mastiff may latch onto his arm with a tight grip in order to warn him away. Never train a mastiff to attack another human being. Typically, if you treat someone as a friend, after a few visits the mastiff will also accept the guest's presence.
Behavior with Family
Mastiffs make great family dogs. Despite the animal's large size, behavior is usually relaxed. Accommodations, such as a large backseat for transport, will need to be made because of the mastiff's size. Qualities that make this dog a great pet are its patience, affection and loyalty to its family. It also is typically peaceful with other animals and humans.
Behavior with Children
English mastiffs seem to understand that children are like puppies and must be treated gently. Like most dogs, the mastiff may let a child know if the child is behaving too roughly with the dog. In this case, the mastiff may gently grab the child's arm to warn her. Teach children to be gentle with the dog, and the mastiff will respond in kind. Although a large dog, the mastiff can be trusted to look after children with loyalty.
Ideally you should bring up a mastiff as a puppy so that it is used to being around children. Even if a mastiff is introduced to a family with children at a late age, it can still be trained to respond to children gently. Teach children to be kind to the dog, and train the dog to respect the child as it does adults. As with strangers, the dog will grow used to the presence of a new person and respond well to affection and kind words.