Are you letting them keep the fruit? I've lost both nectarine and peach because I let them keep fruit on 2nd year and they were too weak and didn't make it through winter. Now we're striping all trees for at least first 3 years to make sure they are strong enough.
I heavily pruned my peach trees after they blossomed. One seemed big enough to actually fruit well. But I wanted the branches to go a different way so they got pruned way back. I'm sure I won't get fruit. But hey its just their second year so I'm fine with it.
I'd cheat and let a few of them mature :-) I'm one who feels if the good Lord didn't want them to grow fruit, He wouldn't have given them blossoms, but I'd thin the fruit out to just give me a few to enjoy.
Everyone, I normally just worry about good root growth during the first couple of years, but will likely allow 10 fruit on each tree to reach maturity. Really deep watering every 10-14 days should help them get through the winter, Jenny
that winter all trees (and everything else) was in 3 feet of snow from November till March. :(