Last year I grew little peach trees in my office and then transplanted them after the frost free date for my area of Indiana. To give them the longest growing season possible for their first year, I started stratifying the seeds in October, potted the seeds in December, and by Christmas had little trees pushing out of the ground. When transplanting time came around in early May the trees were 12-18" tall. At least in my area, the two major risks for a newly planted tree are rabbits and drought. A tree guard will help protect against the rabbits, and by watching the weather you can tell pretty easily if a couple gallons of water would really help out the young tree.
When you plant these out, it would be great for the babies if you did the initial watering in with some B-12 to stimulate their roots. John gave you the timing and protection from critters info.
To make your own B-12 just take 2 B-12 vitamins and dissolve in a gallon of warm water, let this cool completely before you give your little trees their first in the ground drink.