Mastiff Info Please

I brought an em pup into a family of kids, a siamese and an 11 yo alpha sprnger spaniel-successfully.

1.  I immediately placed him in a puppy kindergarden class (aka basic obedience).
2.  I allowed the kids to put their hands in his food while eating and 'treating' to prevent him being aggressive.  cannot imagine a 200 lb snapping at my kids.
he has been awesome and totally puts up w/ the loudness and chaos that my kids bring-even some of the antics!  amazkngly, he has the ability to 'alter' his level of play depending upon the age and ability.
4.  the cat tolerates him.  the springer tolerated him as well.  we socialized him weekly by introducing him to ALL critters (even frogs) as a small pup so now, at 170lbs, he wouldn't harm a treefrog -literally!  even on our irregular walks, he has been assaulted by chihuahuas and his disposition was like-whatever.
5.  exercise?  we live in a small home and he is content being asleep under our feet!  very low activity level!!!  however, when I'm in a walking mood, he is all  but screaming 'lets go'.  the bottom line is they adapt to your level of energy.  they don't require a lot of space but they need daily interaction and play.  we spend a few hours a day outside playing get squeaky man. 
6.  be prepared to decorate around the wobblers and the slingers!  they get everywhere.
7.  easy to housebreak and train.
8.  to help with bloat, we feed him small meals 2 times a day and keep his kibble small....he doesn't suck air and  actually grazes nicely.  this helps keep him lean, which helps keep him healthy and free of hip issues thus far.  8.  heartworm meds are based on weight so he costs more for 6 mo supply.  they are low groming need (puppy trainiiing taught me how to clip nails and how to get him to let me), food costs are high due to the amount he eats a day....but he doesn't like the more expensive foods so we r lucky that beneful has been his favorite and he thrives beautifully!

good luck and hope this helps.  I think that if you are home a lot and can handle the size, a mastiff is a beautiful addition to a human family with kids and other furry friends!  I would NOT recommend adding a mastiff if he would be left alone, as the breed needs their people!  I refused to go back to work until mine was 2 and even then, I only work 20 hours a day.