It would be a good idea to pot up each of the individual oak trees into their own containers (a deep 1 gallon container should do for the first year. This will keep those that are unhealthy from affecting the others and allow for the roots of each tree to grow without impeding or getting tangled with the roots from the other saplings. It's best to use a bark-type potting mix, one that is made for trees and shrubs. You might be able to purchase this from a local nursery. Once the saplings are potted up, they should be watered well and put in a location outside, but well protected from the cold winter temperatures. In the nursery trade, these containers are placed pot-to-pot and usually covered with insulation of some sort and kept in a cold frame or overwintering structure that keeps temperatures cool, but not much below freezing. You want the trees to go dormant but also want to keep the containers from freezing. They will need to be checked and watered every few weeks during the winter to make sure that the containers have not dried out. They will not be actively growing so the containers may stay fairly moist throughout the winter. In the spring, when temperatures warm back up, you can remove them from their protected location into a sunny location and continue to water them, more frequently in the spring.

You can grow them like this in the container for a year and can plant the following spring or if you feel they are big enough, you can plant in the ground this coming spring. Be sure to put some caging or protection around saplings planted in the landscape to avoid mowing over them or having them get damaged by wildlife.

I tried to identify the type of oak tree from the photo, but would like to see pictures of the acorns to be sure. Young leaves can be deceiving but I am leaning toward an English, Chinquapin or a chestnut oak.