Hi Melinda ~
I feel the force is strong with your youngling and he picked a most excellent "best buddy".
Yoda does not appear at Hollywood Studios for meet and greets. In past years, there have not been any opportunities during Star Wars Weekends (SWW) For meet and greets either. That could always change but right now Yoda isn't making meet and greet appearances.
You can find Yoda related merchandise at
Tatooine Traders including T-shirts, toy figures and plushes. They have them throughout the year and not just during SWW. You'll find Tatooine Traders next to the entrance of Star Tours. Conveniently, Guests who experience Star Tours exit through Tatooine Traders. There is usually a merchandise cart across from Tatooine Traders near the photo op with the Imperial Speeder Bike that sometimes carries some Star Wars merchandise so you may want to check that out as well.
Please feel free to keep the questions coming. We are hEAR to help!
Wishing you minnie magical memories :-) Allison V.