I found this too on the website:
If a minor child is travelling with one parent only
The child should have:
a copy of their birth certificate, and
a letter of authorization, in English or French if possible, and signed by the parent who is not travelling with them.
The above letter should give the address and telephone number of the parent who is not travelling. A photocopy of that parent's signed passport or national identity card should be attached.
Also:
If the parents are separated or divorced, and share custody of the child, the parent travelling with the child should carry copies of the legal custody documents. It is also best to have a letter of authorization from the other parent who has custody to take the child on a trip out of the country.
If the parents are separated or divorced and one of them has sole custody of the child, the letter of authorization may be signed by that parent only and they should bring a copy of the custody decree.
If one of the child's parents is deceased, the travelling parent should bring a copy of the death certificate.
I just wondering , how bout if the father not around anymore, what I mean is he never bother him self to care to the child & can not locate where he is, he don't have communicate at all , totally abandon something like that, so what the best thing to do? 
