Birth records typically show when a person was born, the location of their birth, and the names of their parents. These records are essential in establishing parental relationships.
1) Birth registrations
Birth registrations were required by the Province of Ontario starting in 1869. These records are the first documents in a person's life, and effectively establish an individual as existing (for the purposes of government bureaucracy.) Many times there is a lag time between date of birth and date of registration, since it may have been difficult for the parent's to get to a registration office if they lived in a rural community. Sometimes the difference can even be years.
A birth registration (a public document) is necessary to obtain a birth certificate (personal document.) A person must first be registered with the province in order to be issued a certificate confirming their birth. Birth registrations are closed records for a certain period of time in order to protect the privacy of citizens. Each year, the Office of the Registrar General transfers another year of records to the Archives of Ontario which in turn makes these records publically available. Thus, birth registrations for the Province of Ontario are only available from 1869 - 1916. If you are looking for a birth registration after 1917 you will need to apply for it from the Office of the Registrar General.
2) Birth Announcements
Another resource to obtain a birth record is a birth announcement in a newspaper. Many local newspapers are indexed so that you merely need to consult the alphabetical index to find the issue of the newspaper in which the announcement appeared. A tip for Lambton County birth announcements is to check the Sarnia Observer as it was and is the largest newspaper in the region, as well as the smaller weekly newspapers for the community in which your ancestor lived.
3) Church Records
Another resource for birth records are Church records. Church records are often the only resource for pre-1869 births.