As a worried neighbour, could this be a dangerous dog?

I have recently moved next to a property with 2 dogs, one rotty who seems ok but is kept in a small cage all day and stresses and whines, but the other is a bull mastiff who attacks the fencing and continuously barks and growls at us, or is also kept in the tiny cage all day and barks. Other neighbours have been confronted by this dog and say is it over protective and dangerous. I have a baby and a 4 year old, should I be worried? I always thought Mastiffs were gentle giants?