We are having a really tough time with Jessie on walks. She is walked off lead every day, and when I walk her on my own or with a friend and another dog she is amazing. But whenever we walk with our children who are 6 and 8 she seems to get nearly nasty. If they run off she used to heard them up, and sometime this would result in her jumping and grabbing at their clothing. But in the last week or so she is doing this even when they are near us, and what seemed protective and playful has become distressing. She has hurt them by grabbing them. We always say no, and the children do too in a deep and authoritative voice, and I then put her on her lead. She has done this to a lesser degree to friends children too and I am really worried about it. Is it puppy play that will stop or something to be much more concerned about? Jess will be six months old next week. Thank you......