Start by formulating a relevant question which has one or more answer.
Your statement above would be one of many possible answers. Possible questions would be:
1. What is causing children in order to become trafficked?
2. Who is most the culprit when children are trafficked?
Then start a story to your essay of a child (real or imagined) who is trafficked by their parents. Next tell the statistics of trafficking of children. End that first paragraph (or it could take 2 paragraphs based on how much information you have) with the question above. The paragraph that is next tell a few of the possible answers that other individuals might give, and then tell your answer in a sentence something like this:
However some social people might blame XX or XX, the truth is, parents are to be culpable for human trafficking of these children because XX, XX, and XX.
Those three reasons after the 'because" will be the basis regarding the rest pay for essay of the argument.