Not needed. I recently travelled internationally with my toddler sans my wife and never had to present any documentation anywhere expect for the toddlers passport.

latiokiller is correct. I have done this too, however, I would suggest you to carry birth certificate. I was asked to present once at Dubai airport. I think they were making sure that we were the parents.

Thank you guys for sharing your experience

I know people traveling in parts of Europe have been asked about this. I wouldn't take a chance just because few souls had a smooth sailing. Sometimes all it takes is a tired officer with a foul mood to screw your trip. Hope you have safe and hassle free travel!

Please google and complete an AFFIDAVIT OF PARENTAL CONSENT For Travel Outside The United States Of A Minor Child Without Both Birth Parents Traveling. You will probably never be asked for it, but my 10 year son needed it in Paris. They sometimes ask for it even when entering from Canada or Mexico. Happy Dashain!

Thank you all for sharing your experience. I will make sure I will carry a consent letter and birth certificate for hassle free travel.