We had a situation just yesterday with our female Labrador that might have scared someone. We were walking home from the park with her, she was on her leash and halti and walking along calmly at heel. As we approached a house with many kids outside playing on the porch and out in the front yard, Bella suddenly went nuts. She starting barking, yelping, lunging, etc. I couldn't get her to calm down and I knew she would scare those kids so I walked her across the street and away from them. She calmed down fairly quickly and I wasn't sure what had set her off like that (very out of character for Bella who loves kids).
My husband and son continued to walk by the house and realized that as you got closer you could hear young puppies inside the house whining. That was what Bella was hearing and reacting so strongly too (she had the same strong reaction to the sound of wolf puppies whimpering on a recent tv show).
You have to have your dog under control, you have to be a responsible dog owner and you can't just let your dog scare people. Even in this case, where Bella's maternal instinct was driving her to act up and she wasn't being aggressive - she still could have scared those kids with her behaviour. She's a fairly big dog and all that noise and lunging is scary looking. It's a dog owner's responsibility to ensure your dog doesn't hurt, scare or bother other people. If you can't do that, you simply should not own a dog.