[JoeyP]

Yorkies are prone to lunge and jump at small quick moving objects
.... and that is exactly what a child is and Does
This kind of behavior can be stopped
But you'll have to put some effort into it
First get some children volunteers
Have them come in and play with your dog
Be on guard and watchful for any bad behavior
Most likely your dog hasn't be accustomed to children around him
and this is a new and likiely scarey thing for him