Roland, what you have pictured there is not the dreaded leaf curl. Those pics make it look more like the tree isnt getting enough moisture, soft of how corn looks late in summer with the lack of rain. The pale leaves even though they are good sized, also indicate a lack of nutrition. At this time of year you dont want to fertilize any more, but next spring, use a water soluable fertilizer like miracle grow(Walmart brand is cheaper).
Getting fruit trees from seeds is always a crap shoot, you never know if they will grow true to the seed.
The disease of leaf curl can get to other trees, but it is not a killer in the short term. I wouldnt pull out or cut down a tree that had it.
Since you have nothing invested in them other then time, let them keep growing as best they can. Since they are small, try to get a fence around them to protect them from critters. Bunnies will love them in teh winter when it snows if they arent protected.
Next spring when they leave out, start pulling off the leaves from the bottom and cut the top off down about 2 leaves. what you want to do is force branches out from 4 leaves at different sides. Dont worry if you then that grow out, they can be trimmed off in another year when you try to balance out the scaffold branches. You should know in another 2 years if the trees are worth keeping.
Here is a pic of leaf curl, the disease