Once you see green leaves, the plant can benefit from nutrients in the soil but young plants need very little fertilizer, it really depends on the growth rate of the plant. A plant such as tomatoes which grows vigorously can use much more fertilizer. Young plants are extremely sensitive to over fertilization so it's safer to use organics or dilute fertilizer applications.
Often the nutrients already in the soil are enough to sustain a young plant depending on the soil you use. Improper fertilization can lead to nutrient lock within the soil so I feel that foliage applications with dilute fertilizer is best.
Simon