A "Yum Yum" tree is a variety of nectarine which is a non-fuzzypeach. Our little tree is loaded this year and they certainly live up to their name.
They are almost as fun to pick as they are to eat. They all look the same and these two in the picture aren't quite ripe. Several gimes a day we go out and fondle the fruit to see which ones are soft, giving in to a gentle pinch. Those that meet the "pinch test" get picked and usually eaten right on the spot. A little advice, though: if you ever find yourself lucky enough to pluck a ripe yum yum, be sure to lean forward before you bite into one or it will drip down your chin and onto your shirt.
And....YES! They are every bit as sweet and "juicylicious as they look.