Personally, I would worry. My parent's had a Rottie--very sweet dog who went through two levels of obedience training and I still would NEVER trust her around strangers or children. Even trained Rotties seem a little unpredictable to me....
I would NOT be at all comfortable with what you've described.
Never trust another families dog out "playing" with kids not in that family. Period. The dog could be trained so well he does their banking for them--that doesn't mean he won't see roughhousing between your kids and the his kids as a threat to HIS kids.
ITA w/Shannon. The dog is likely only good w/her kids because they are part of his pack/family. I would be uncomfortable around a dog w/no training like that and wouldn't allow my kids around it. The fact that he's so huge and can do so much damage is even reason more. There is only one kid that I let around my dogs w/o my constant supervision and that's because my dogs love his mom (they would never mess w/her pup!), they think he's part of our family, and he behaves really well around them. All other kids I closely observe and some, if they act innappropriately w/the dogs I just don't allow around them at all.
Honestly, it doesnt' matter what kind of dog it is, of course some dogs will take much longer to inflict serious injury, ie, a pug may need a couple hours to maul a child but most dogs will protect their own kids--dogs do not have the thought process to sit back and say "oh, this time they're just playing"
These links are from a story here where I testified as an expert witness. This dog had not shown signs of aggresion and was a family pet living indoors and raised with children. It was my opinion and the opinion of 3 other trainers who testified that there was actually NOTHING wrong with this dog, he just read the signals wrong and had no adult there to look to for guidance.
As a rott owner I would say that I would be uncomfortable with a neighbors large dog growling at me (Rott or not). Rotts can not go without training. My dogs are some of the sweetest Rotts you would ever meet. But I control their world. They do not go anywhere without me there to correct any misbehavior. I would strongly recommend to your neighbor that they get this dog into obedience school now. Tell her that its growling at you made you nervous and that until thier dog has some obedience training that you don't feel comfortable with your son being anywhere near that dog. Her son is still welcome to come over and play with your son. And they can play outside if that dog is inside. Period end of story
I would be very, very nervous. I don't think you are being overprotective at all. I think people are being overprotective all the time on MDC. But not this time.
Sounds like he isn't well trained. You don't have a fence - and even a fence around your yard wouldn't really make me sleep easy. I think that everyone who has mentioned the dog misinterpreting your kid playing with the neighbor kids - tag, wrestling, anything really - as a threat to "his kids" is right on. Just absolutely too dangerous.
It is a really sad situation. I would keep my kid in the house at that age - unless I was with him, or another trusted adult who understood that the dog was right across the street. I absolutely would not let my kid play at their house - inside or outside. Huge bummer.