For the kids, apply for their proof of citizenship, see
http://www.cic.gc.ca/english/citizenship/proof.asp If you would like to get them Canadian passports as well, you can get that though the Canadian embassy in the US after you have applied for their proof of citizenship.
To sponsor your husband, you do not have to show that you can support him but to do this without being in Canada, you need to show some proof of your plans to move to Canada when he gets his PR. This could include having a job offer, having arranged housing, having been accepted to college and failing all of that, at least some letters from friends and family stating they know of your plans and will support you and offer you a place to live while you look for housing and something about what your plans are once you move to Canada. You can find sponsorship forms at
http://www.cic.gc.ca/english/information/applications/fc.asp