I'm on my way out of town for the weekend, and just got your message. I can't respond in detail now, but I wanted to give you a little information off the top of my head.
I'd never heard olive leaf extract before my doctor prescribed it in December,. So I'm pretty new to all its uses, and don't know if it would be useful for your son or not. Ours is in capsule form, and came from my doctor. It is by Segate Products. It looks like you can purchase it on the web here: http://www.seagateproducts.com/olive-leaf-extract.html
My son easily swallows it whole with water or a smoothie.
From what you described, it really does sound like your son has a problem with yeast. Mine did, too. A web search with the terms "candida" and "toddler" may give you a wealth of information and perhaps a place to start.