First how old are your chicks? Are they showing signs of needing to be wormed?
Garlic has been used as a natural way. You can make a garlic concentrate which can be mixed in with the water along with adding food grade DE to the feed. The garlic and DE method should then be repeated a week later. Cayenne pepper is also often used in protecting the flock against parasitic worms.
A natural product called Verm X can be used. In their own words, 100% Natural Herbal Formula with NO withdrawal period for eggs or birds. Here is their link: http://verm-xusa.com/poultry/cat_6.html