This can be stated in active form. AT: "for God will call them his children" or "they will be children of God" (See: [[rc://en/ta/man/translate/figs-activepassive]])
Here "kingdom of heaven" refers to God's rule as king. This phrase is only in the book of Matthew. If possible, keep "heaven" in your translation. See how you translated this in [Matthew 5:3](./01.md). AT: "for God in heaven will be their king" (See: [[rc://en/ta/man/translate/figs-metonymy]])