Is it permissible to sell anything from the Zakat-ul-Fitr to buy things for the house and clothes for my children?

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.

Once you receive Zakat-ul-Fitr from its giver, it becomes your own property if you are one of its recipients; and in this case you are allowed to dispose of it in any way you like, provided that it is permissible, be it selling or otherwise.

The scholars of the Permanent Committee said about the ruling on selling Zakat-ul-Fitr:

If one who takes it as its rightful recipient, he is allowed to sell it after receiving it, because by receiving it, it becomes part of his possessions.

Allah knows best.