Here information would be the best protection. Use isolation methods which do not permit the growth of Clostridium tetani . While you probably don't know the conditions that favor Clostridium tetani, it would be simple to read about them before you begin such work. One goal of this website is to provide or guide you to such safety information. Deciding which experiments are safe for a child are up to the parent and parents' attitudes differ.
Some parents let childern begin driving farm machinery or automobiles earlier than others.
The answer often depends upon the maturity of the child and other local factors. I felt the opportunity to teach my son safe methods for working with electricity, chemicals, and swimming equipped him with skills which benefited him more than the risks involved. For example would teaching a child to swim cause him to become more interested in swimming and tempt him to go swimming alone in risky situations. I can't say for your child. We all face decisions in life involving risks such as buying a new car or keeping the old one another year when the brakes are of uncertain quality.