Does your soil say it has time released nutrients? Many soils like Miracle Grow do and that can be difficult on your young plants.
Posting Pictures will really help those with much more knowledge than myself help you. It is difficult figuring things out without knowing how old the plants are, what lighting your using, what soil your using, are you watering with tap water etc.
The more information you can give the better the response will be and the easier it will be to figure out your problem.