This article is from the Childhood Vaccinations FAQ, by Lynn Gazis-Sax firstname.lastname@example.org with numerous contributions by others.
If they haven't been vaccinated at all, see the answer to question
2.22.2. If they have been vaccinated, then a tetanus and diptheria
booster is recommended every ten years (or five years in case of a
very dirty wound). People in certain high risk groups are advised to
get flu shots annually (see the section on the flu vaccine).