Dogs and Kiddos?

Most dogs are wary of kids this age or they are too stimulated by the child's movements and high pitched voice and play too rough.  Here's a link below to a good article from a repsected veterinary behaviorist for ways to teach kids how to interact with a dog. 

 I know your son is quite young but the concepts are similar to how he's learning to interact with other children and adults and it's a good life skill to teach early.  You're wise to recognize that your dog isn't comfortable and to see how to help her be more comfortable and to keep your toddler safe.

http://drsophiayin.com/blog/entry/kids-and-dogs-how-kids-should-and-should-not-interact-with-dogs

 Toddlers tend to jerky movements, they don't have much routine to where they go and when, and dogs sense this.  It makes them uneasy.  I wouldn't force your dog to "like" your son.  I haven't clicked on the link provided (yet), but you can work on "supervised" sorts of interactions, holding your son, with a treat he tosses to the doggie, and then let doggie leave again.  Let the dog feel it has some control and can move away at all times.