Children are the most vulnerable and hardest hit among the world's migrants and require special protection, Pope Francis said.

"Children are the first among those to pay the heavy toll of emigration, almost always caused by violence, poverty, environmental conditions, as well as the negative aspects of globalisation," he said.

"The unrestrained competition for quick and easy profit brings with it the cultivation of perverse scourges such as child trafficking, the exploitation and abuse of minors and, generally, the depriving of rights intrinsic to childhood as sanctioned by the International Convention on the Rights of the Child," he said.