I don't think visit visa will be a problem in terms of application. Its not that you should be eligible to apply them - don't confuse this with spousal sponsorship. Your children should show that they will go back after their visit ends, that is the main criteria. Here's what CIC says:
To visit Canada, you must:
have a valid travel document, such as a passport,
be in good health,
convince an immigration officer that you have ties—such as a job, home, financial assets or family—that will take you back to your home country,
convince an immigration officer that you will leave Canada at the end of your visit, and have enough money for your stay. (The amount of money you will need can vary. it depends on things like how long you will stay, and whether you will stay in a hotel or with friends or relatives.)
You may also need a:
temporary resident (visitor) visa, depending on your citizenship (see Find out if you need a visa),
medical exam and
letter of invitation from someone who lives in Canada.
Whether your kids will get the visa or not is a different story. It may seem to CIC that they will come to you and simply stay indefinitely illegally. So, please focus on attaching evidence that they will, and need to, definitely go back to their country after their visit.