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Since you saw your son provoke the dog, I would not be overly concerned about agression unless it happens again.
I do suggest that you only allow them to play together when you can supervise. Dogs can quickly take over in situations with young children because they consider them to be their equals.
English setters can be pretty headstrong so you need to start an obedience class if you have not done so already. Involve your children in the training.
As far as the bite goes, you can use a little antibiotic ointment and contact your pediatrician if you have concerns.