Are you taking children across an international border?
Does the child have their own current valid passport?
Does your child have the same last name as both parents?
Child trafficking conventions and strict laws against the unauthorized movement of children could be a problem for your travel plans. Such rules were put in place to help stop the theft of children by strangers, traffickers, relatives, and lone parents abducting their own child.
More and more children in Canada have the same last name as only one parent, or even a different name altogether in the case of children living with a guardian.
It is always important that when a child has a different name, and I mean different in any way at all from either of the parents, that the parents carry along the provincial government-issued LONG FORM BIRTH CERTIFICATE. This long form birth certificate lists the names of both parents in full, and is a most valuable document for proving the real relationship of the adults to the child.
Some embassies require a copy of this document before issuing a visa to a child. Other countries will issue a visa, but will demand proof at the border.
In some cases you should strongly consider have a lawyer sign and notarize a letter stating the names and relationships of the adults (parents or guardian) to the child, and to have this with you while crossing a border.
Be prepared with documents, not turned away from the border.