3 yr old female aussie herding/nipping children

Question
Hi,   I have a 3 yr old red merle.  She does nothing wrong,except she does not like children.  We go to a private dog park where children are not allowed,however, every once in a while other members let their children in.....and I am not aware they are in the area.  Salsa will circle a child and when it runs will nip it in the back...has not drawn blood, but leaves a bruise.   I have taken her to a dog trainer here in Columbus, OH who wants to keep her 10 days and redirect her thinking.  I am very concerned about this.  She is a one person dog, in fact I have 3 dogs of different breeds and they are all "My dogs".  She has been obedience trained and intermediate agility trained. She has been evaluated on sheep 3 times and does extremely well, so I know she has a strong herding instinct.  If I do not go for outside help,  how do I start?   Take her to playgrounds and sit with her?  If I say stop and she doesn't roll her ?  Both have been suggestions from trainers.    I am not sure where to start?
Thank you

Answer
Kathryn, I would also be VERY concerned about leaving your dog at any boot camp type training arrangement, because they often use very harsh methods.  Janel Biglin is in Columbus and is a force free trainer.  You can find her listing at Pet Professional Guild.