is that a one-off incident? Meaning, has she ever growled at you before, not counting play growling? If she has never done that before, you probably do not have a problem on your hands, just a startled puppy. But I do understand your concern with the kids - it is funny how things change when you have young children to protect. We had a Wheaton Terrier mix that I raised from nine weeks of age with my three children. Our pup was not allowed on the couch or through the door first, was hand fed by the kids with me supervising, did wonderfully in obedience class, played with the kids beautifully. Within a week of turning eight months of age, he growled at my then-three year old as he walked past him while he was eating. I could not believe I heard him correctly and thought it was his tummy growling, until he did it again the next day. A couple of days later he was chewing a tasty bone and when my daughter walked by he bared his teeth at her, snarling and growling. As soon as I saw that my heart just broke, because, if any was to ever happen after that moment, I would have to live with knowing that I saw the signs and chose to ignore them. We placed him in an adult-only family who were going to work with a trainer to help him overcome his resource guarding, with the knowledge it was most likely his temperement that contributed to his behaviour.
