Would I be committing a sin if I abandon my son, whom I fathered through a temporary marriage, in order to avoid family and social problems?

The question has two possibilities: If the marriage was concluded with its conditions and pillars, then the marriage is valid, and the child is attributed to you. However, if it was a Muta'h marriage (temporary marriage), then the marriage is invalid by the consensus of scholars. Nevertheless, if you entered into it believing it to be permissible, then the child is attributed to you. In both cases, this child is yours, and you are obligated towards him as you would be towards any child. It is not permissible for you to disown him or neglect his rights.