If you want to immigrate without a sponsor, then you'll need to qualify through one of the following immigration streams: Federal Skilled Worker, Federal Skilled Trade, Quebec Skilled Worker or one of the Provincial Nominee Programs.
You can read more about these programs and their criteria here:
http://www.cic.gc.ca/english/immigrate/apply.asp
Having two Canadian children doesn't help you - unless at least one of them is an adults who is working in Canada and making sufficient money to qualify to sponsor you as their parent through the family sponsorship stream.
