Here "kingdom of heaven" refers to God's rule as king. This phrase is found only in the book of Matthew. If possible, keep "heaven" in your translation. Alternate translation: "for when our God in heaven establishes his rule on earth, he will be king over such as these" or "for God will allow such as these into his kingdom" (See: [[rc://en/ta/man/jit/figs-metonymy]])
"belongs to those who are like children." This is a simile that means those who are humble like children will enter God's kingdom. (See: [[rc://en/ta/man/jit/figs-simile]])