Answered by Irving I. Gottesman, Ph.D.:
A context for understanding the implications of your important question can be found by reading the brief genetic counseling pamphlet I wrote for NAMI with my co-author Dr. Steven O. Moldin of the NIMH.
Your question and others dealing with the risk for developing schizophrenia in the future for a relative of a consumer with a verified accurate diagnosis of this disease requires an individualized answer after a face-to-face review of the facts. An approximation to the correct range of risk values will depend on such things as the pedigree structure of the family out to second degree relatives (grandparents, aunts, uncles) counting not only the ill but also the well. The more healthy relatives, the lower the risk.
Please, in your situation, do not spend the next 20 years "waiting for the other shoe to drop" as that is, on average, not likely. As a ballpark figure, consider that the average risk to nieces and nephews of a patient after they become adults is under 3%; the risk to a random member of the general population is about 1%. I would suggest that it is much more practical to protect your child from the more common risks associated with tobacco, street drugs, and alcohol -- by example and with a strong school-based education program in healthy living.
You may wish to consult the useful Web page set up by the National Society of Genetic Counselors and look for an agency nearby, especially one that specializes in complex disease such as diabetes, heart disease, and other complex diseases involving genetic predispositions plus non-genetic contributors.