In addition to the above information, according to Dr. Spock at drspock.com, "Rectal suppositories are not generally the first choice at this age. However, they are very quick and easy. More than half the parents I talk to shudder at the thought, and there are definitely toddlers who won't tolerate insertion of a suppository.
However, when children are very sick, vomiting, or refuse other forms of medicine, this is a reasonable alternative if medication is necessary to bring down a fever."
For more information read, "Fever: Nine Months to Three Years:"