The most likely cause of stunted plants is the root damage done by over-watering, especially if you have been experiencing all the extra rain that has affect much of the country.

None of us ever think we are over-watering yet we are. When we make ourselves cut back on it the plants always seem to improve. And when someone says "plenty of water" I immediately cringe and think over-watering since tomato plants don't need much to begin with. :)

So assuming the plants have sufficient nutrients available in the soil - their color in the pic isn't good - then my best guess is poor root developments from being too wet. It can't hurt to give it a try - cutting your watering in half - and see if they don't perk up.

Dave