A dog is a great companion for a child, especially an only child. They don't have anyone to play with or talk to, but at least they have a dog. That's good enough to build some social skills. If you wonder why some people kiss with so much tongue, it might be because they were an only child with a dog. We could go on with the examples, but they only get more disturbing from there.
The other great thing about having a dog is that they can double as coloring books. Take this dog for example. One second you can be playing fetch, the next second you can draw your favorite superhero on him. That's versatility if I've ever seen it. Just make sure to get a white dog so you have a blank canvas to play with.