I wonder how the little girl expressed her dislike?
Not excusing the barking - your son's running and crying could have triggered prey mode (?).
Biting the ankles - it may have appeared aggressive - is it possible the dog saw the toweling as play and decided to play his style. Again, not excusing but throwing out ideas.
Definitely keep a leash on your dog for easier control and monitor ALL interaction with your son
In addition to the trainer, more good links
Family Paws-New parent classes dog and baby
Also, do a search on here for the 2 week shut down