I was diagnosed with Raynauds while I was taking a medication. Don't remember which one. When I stopped the medication my hands were once more warm and not blue.
It's my understanding that the actual cause of Raynaud's is unknown. I recently read of a toddler having it but don't remember where. The medical person answering the question said it's not something to worry about.
I urge you to do whatever you need to do to reduce your concern. Stress makes the symptoms worse and your son will pick up on your tension. Also it does not help to worry and only makes life miserable for you. I have found from many years of living that it really is true what some political figure said: "The only thing to fear is fear itself." Every thing that's happened in my life, including lung cancer, has been OK. I've learned and grown from every experience.
I read a couple of articles that I found on the Internet and I suggest that the conditions that can cause Raynaud's are not likely to be seen in a toddler. However, if you're still concerned, make a list of the conditions that concern you and perhaps his doctor can either do a test to rule them out or reassure you that's it's unlikely for your son to have them.