The use of herbs, traditional medicines, flavor enhancers and even charms to ward off evil spirits, is one of the many topics explored in Things of Science, a mail-order science service for children 10 to 16.

Each month, subscribers receive a different kit containing a booklet and a number of demonstrations to try made out of inexpensive materials.

"I hope to get children interested in science topics so they will want to explore further on their own," said Donald I. Sparks, president of Things of Science.

Gastropods (sea shells), color, curves, bubbles and sun dials are among of the many science subjects that children, teen-agers and parents can investigate. The kits can be used as a hobby, as ideas for science fairs, as supplements to school work or to help decide on careers in science or mathematics.

"I have been a subscriber to Things of Science since I was a small boy," Sparks said, "and I used to help out writing the kits when it was a part of Science Service, which publishes Science News magazine." Sparks bought Things of Science (in existence since 1940) from Science Service in 1978.

Subscribers to the service are as varied as the topics. "I had one man in prison who did this as a way of keeping in touch with his son, and I have a number of foreign students interested in science who use this as a way to sharpen their English," Sparks said.

A one-year subscription costs $20. Write: Things of Science, 819 Washington Crossing Rd., Newtown, Pa. 18940.