Did you ever notice the difference between these two words? Obviously both of them pertain to pain. Many parents have used these words to comfort their kids and somewhat try to show them that they know what it feels like. They are speaking "Child". Now these two words may seem closely related but they're used for two very different types of pain.
Ouchies - Ouchies is mostly used when a person or persons gets a scrape or gash in their derma causing blood. For example when someone falls off their bike and scrapes their elbow a bystander may say "Ouchies!" to express his/hers understanding of the pain.
Owwies - Owwies is most commonly used when one has a sore stomach, headache, or any other type of non-visible pain. For Example if one had sore muscles he/she would express this by using the word "Owwies". It is most commonly used when sharp pain is recieved usually from a quick movement or loud noise.
Right now I have the worst sore stomach in the world. Basically, I have all the symptoms from the pepto-bismol commercial... Yes it's horrible. Tommorow morning at 7:00 I leave for a 12 hour trip to Kuujjarrapik so I'm hoping that this sickness disappears soon!