I don't know if the trees will come back without seeing them, but they probably will unless the deer ate the bark on the trunk all the way around. It the trees have been girdled in this way, they are probably not going to recover. To combat deer there are no plants you can grow to keep them away. In deer country, you must surround young trees with a protective ring of woven or chicken wire. Once the trees have a few years under them, you can remove the barriers. You can also try spray repellents. Liquid Fence makes a deer repellent that some folks have had luck with. You can buy it at Home Depot, Lowe's, Wal-Mart, etc. But, it needs to be reapplied after every rain, etc. Your son's only sure method of deer control is with the barrier."