Just give them a little more time. I think they'll come around. Tomatoes are fickle. They want the soil to be a certain temperature when they're planted, another when they're growing during the day, then another temperature by night,. Lots of moisture, but not too wet. Tons of foliage, but not too much or a fungus will set in, too little and you'll get sun scalded fruit. Are they in the greenhouse, or outside it? If they are outside, you can extend the growing season by the use of a frost blanket.....What variety is he growing?