Bringing a baby into a home with a large dog...

Just wondering if anyone here has large dogs at home with kids and how do you set boundaries for them without causing aggessive/ jealous behaviour?  I have a medium sized border collie and a few years ago I rescued an english mastiff who is 200 lbs.  People have remarked "If you have kids you will have to get rid of that big dog."  Well the big dog is a permanent member of the family BUT he can easily knock over an adult...anyone else in the same boat? My main worry is the dogs have full run of the house if and when a baby comes along how do I introduce them?  How to keep 2 curious dogs from keeping their distance without feeling like they are in the proverbial dog house??