Hi there, your best bet is to talk with a CFP and/or insurance agent. There are so many options available.
If you are on a limited budget and looking for insurance to help them in the event something happens to you, the least expensive option would be a term life insurance policy payable in the event of your death. You can purchase a 10, 20 or 30 year term policy relatively inexpensively (premium is based upon your age, weight and other health factors). It is possible to get several hundred thousand dollars coverage for around $50 per month.
If you are looking for insurance for the kids, you can purchase a whole life policy that has a small cash value after paying premiums for several years. For instance, we purchased $100k whole life policies for our children shortly after birth and we pay premiums of about $100 per year (similar to the gerber plan).
We personally carry a combination of whole life policies and term policies for my H and I, and whole life policies for the kids. Our term life insurance policies will expire when H and I are in our 60's. To renew the coverage on them would be quite expensive, however by then both kids will be (should be) out of college and on their own. We have managed to save quite a bit through the years so those policies won't be necessary any longer. Our whole life policies will still be in effect to cover funeral and other expenses (the premiums do not increase on whole life policies).
Sorry this is so long.....contact a local insurance agent and have them give you quotes for the different types of policies. Discuss what you hope to accomplish with the insurance and they will be able steer you in the right direction.
I think it is great you are thinking about your kids security. We had a dear friend pass away unexpectedly who left very little insurance. The last few years have truly been a struggle for his wife and kids.
Best of luck to you!