Im dont own a rottie, so ill speak from taking the rottie that stays 3 doors down for walks,

He was bought from a proper breeder, the dog owner has bought 3 dogs from the breeder over the years, has had no trouble with any of them

He let it get used to young children(his 2 grand children esp) from the day he got it, he also trained it, but showed it that he was the boss and the dog would respect him.

The dogs just over 2 years old. hes huge and a big friendly mutt. ive taken him for walks and had no problems, he sits at the side of the road, and will stay there untill i give the command for him to walk across the road.

Buy one from a proper breeder, let it get used to children and people, train it well, see a proper trainer if you dont have 100% confidence in your own abilities. and you shall have a great dog for many years