As-SalamuAlaykum! I have a child born to a woman who had accepted Islam but then apostatized and ran away, taking the child with her. Since then, I have never seen my child or heard anything about him. Shall I pay zakah Al-Fitr on his behalf? Please advise me. May Allah reward you!

All perfect praise be to Allah, the Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.

You have to pay zakah Al-Fitr on behalf of your child, even though you know nothing about him. This is because your child is assumed to be a Muslim in relation to you. In Mughni Al-Muhtaaj, the author says:

A child should be considered a Muslim if both or one of his parents was a Muslim at the time this child was a clot of blood in his mother's womb. That a Muslim parent comes to renounce Islam after the formation of the clot of their future baby should not affect the fact that this baby must be considered Muslim.

Moreover, the basic rule is that your child is assumed to be alive until proven otherwise. This means that you have to pay zakah Al-Fitr on his behalf until he reaches the age at which you believe he would be able to earn his living, in which case you no longer have to pay zakah for him. You should take every possible measure to find your child so that you can bring him up according to Islamic teachings and teach him what he is required to learn thereof.

Allaah Knows best.