I am a Canadian citizen and my wife is a permanent resident of Canada.
We have a 8 year old child born in US ( after I acquired Canadian citizenship).
We are relocating back to Canada after 9 years next month. My worry is will my child be eligible for OHIP ? Because it can be really scary without health insurance in Canada.
The child is a Canadian citizen by default if he/she was born after you became a citizen. You should apply now to have your child recognized as a Canadian citizen asap (this process takes several months to complete). Once the child has a citizenship certificate and has lived in Canada for three months, he/she will qualify for OHIP.
Just to add, you should obtain travel insurance to cover your family until OHIP coverage kicks in. Since you and your wife have been outside of Canada for such a long time, you will need to reside in Canada for three months before you have OHIP coverage. So you will need to purchase insurance to cover yourselves for at three months. You may have to keep the travel insurance in place for your child longer (depends how long it takes to get the citizenship certificate). Note that travel insurance will most likely only cover emergencies. You'll need to pay for any other care you receive.
Yes, you gained citizenship before your child was born and therefore your child is a citizen. You need to apply for your child's proof of citizenship, see http://www.cic.gc.ca/english/citizenship/proof-how.asp
Once you have the citizenship certificate, you can apply for a Canadian passport for your child.