If your children have Canadian citizenship then you can't sponsor them with your husband since they cannot be permanent residents (they're already citizens!). I believe you would instead file for a proof of citizenship certificate for them, and then you could file for their Canadian passports.
Juste a note to add: Children born to Canadian parents ouside of Canada are Canadian by birth if it was before April 17, 2009 when the new rules took effect. "If your children are born outside Canada on or after April 17, 2009, they will be Canadian only if their other parent was born in Canada or became a Canadian citizen by immigrating there as a permanent resident and subsequently being granted citizenship (also called naturalization)." http://www.cic.gc.ca/english/information/faq/citizenship/index.asp