Hi Mikem, and

!
I have put your questions into a separate thread, so your questions get the attention they deserve.

Congratulations on your surprise goldfish fry! With 3-4 cm long, they most likely are already at least a month to 6 weeks old, if not more. Spawning is induced by warming of the pond water, so if your summer days suddenly got a bit warmer a few months ago, that would have done the trick.
Since they grew to their size without you feeding them extra (how could you anyway, you didn't even know they were there..

) they had most likely leftover food from the adult fish, as well as plenty of algae on the pond walls for them to eat. I found surprise fry in our comet ponds as well a while back, and since then I just crushed the regular adult pellets I feed into smaller crumbs and powder, they do well on just that, supplemented by tossing in a handful of frozen bloodworms every so often. Those little fish are survivors, and have so much to eat in a pond - insects falling in, small particles in the water, the walls covered in algae, as well as pond plants.
As to what breed the little ones are - well, thats a tough question. It could be a combination between the goldfish and the shubunkin, or all goldfish, or all shubunkin. At that point its anybody's guess, really. When you look at them, do you see differences in body shapes, or tail shapes?
As for the color, that also widely varies. They will get all kinds of colors, especially if a shubunkin is a parent. I had my shubis breed, and although both parents - naturally - are calicos, the fry turn out black, red, red/white, and white. Only a few got a calico pattern.
What are you planning on doing with them? Your pond surely is big enough to support all of them, especially if you have a filter connected.
Or do you wonna give some away to local pet stores? Friends?
When you decide on a pet store, I would let them grow some more, to about 8-10 cm, otherwise the petstore might consider them "just" feeders and sell them as live food for carnivore fish like cichlids and oscars. With a bigger size, and more brilliant colors, there is less of a chance for the fish ending up as food.
Geez, I hope I covered it all - feel free to ask away with any questions you might have!