Be prepared for drool, but otherwise, but both breeds can be absolutely wonderful with children. The Mastiff is the reason for the drool alert, but maybe they will take after their Mom ... Like any dog, you'll need to invest time in training early on, as you want to especially leash-train the pup before it is big enough to yank your arm off. Start getting it used to the collar and leash right away, and you shouldn't have a problem.

I'd ask to see the parent dogs, at least the mom, which will give you some indication of temperament.