Thats really an odd event! I've never had any problems with my mom's pit-bull's! It's weird that the only two species of in the world that have sex for pleasure would be, us the humans, and Dolphins. Dogs do it for reproductive reasons and its in there nature.
Even if they have no idea why they are doing it. And some dogs also do it to establish dominance through out there peers. kinda weird to think that a toddler did anything to make the dog feel inferior. . .