You probably want to start with a single, quiet child before you go for the playground. Your dog sounds a little high strung/excitable so a playground might be a final graduation kind of exercise. Seeing all those kids running around and yelling might teach her that kids are either very scary or things to be chased and played with. I would start with the child of a friend if thats possible, have them calmly toss treats from a safe distance with the dog leashed. Then when shes totally comfortable (may take a few sessions) move forward slowly until your dogs can smell the little one and maybe a gentle pet. Go slow, don't want to overwhelm her. I don't know the level of fear she has but if there is ANY doubt I would start with a muzzle, better to find it wasnt necessary than to realize after the fact that it was...
I'm not a dog trainer so these are just ideas, the best idea would probably be to consult a trainer/behaviourist.
I'm not a dog trainer so these are just ideas, the best idea would probably be to consult a trainer/behaviourist.