I've frozen fruit for my cherries before and it seems okay but I do prefer giving them fresh fruits. Once you freeze it, the tissues get damaged and are mushy upon thawing. The only time I give them frozen fruit is when I buy one of the big Maradol Papayas that I can't finish and I want to hold back a little for them. Otherwise, it's all fresh baby!
I can't speak for the nutritional values of frozen vs. fresh in any tangible or educated terms, but it makes sense to me that fresh would retain higher levels of nutrition, though it may not be a significant difference. I'll leave this to others with more knowledge on the subject.
"Fresh" is only more nutritious when it is actually fresh. Fruits and vegetables begin to lose nutrients from the time they are harvested. If you can get something locally grown and it is being consumed within days of being picked, then it should be more nutritious. If it is being picked, shipped halfway around the world, and then sitting at the grocery store for a few days before you buy it...the two are probably comparable.
Frozen is good for providing variety during winter.
I buy frozen organic blueberries or strawberries. I have added one or two smushed up pieces to diced cactus pads or mulberry leaves to entice the torts. They love it.