How to fix leggy sprouts?

Wait until the seedlings are large enough to handle and can be potted on. When replanting the seedling, sink it low into the new pot so that most of the leggy bit is below the soil surface. If you like, bury the mistake and often the seedling with grow on with no obvious problems. Give it a couple of weeks and it should grow on fine, should it fail you have lost little other than some time and compost. This method is particularly effective with tomatoes, which like to be re potted deep to encourage the root system and almost always grow on well after this treatment.