He's right, if your children are included on your husband's application before and met the requirements, then it should be fine. Check this link http://www.cic.gc.ca/english/immigrate/sponsor/spouse-apply-who.asp
You may also want to take note of this, it's from the said website:
"Dependent children
A son or daughter is dependent when the child:
is under the age of 22 and does not have a spouse or common-law partner
is a full-time student and is substantially dependent on a parent for financial support since before the age of 22, or since becoming a spouse or common-law partner (if this happened before age 22) or
is financially dependent on a parent since before the age of 22 because of a disability."