When my son started school, we were concerned about enrolling in a French immersion program because he has had speech and language development issues. We were also worried because neither my wife nor I speak French so we weren't sure if we could help him if he had trouble. During the registration we were encouraged to try French immersion anyway and to switch later if he ran into trouble. The school board provided speech and language therapy for him and so far he is doing fine. There is an English stream at his school and the kids from both play together, go on field trips together, etc...
I should note that starting this past year, all kids entering kindergarten are taught in 50% English and 50% French. Only after two years of kindergarten do they have the option of early French immersion starting in grade one. http://www.ocdsb.ca/programs/ele/fi/Pages/default.aspx