«فِي النَّسَبِ فَرْخِي وَفِي الْمُكْتَسَبِ فَخِّي»
By lineage he is my young, but for income he is my snare.
Farkhī evokes a bird's young and identifies the boy as his offspring; fakhkhī means a trap, exploited for gain. The near-rhyme is inseparable from the ethical contrast. “He is my son” misses the second half.
The two prepositional phrases divide the perspectives: family origin and earning strategy. The line reveals how the elder turns kinship into an instrument of extraction. Keep that contrast rather than reducing it to a clever sound effect.
Translation exercise
Divide the phrase into kinship and gain; identify the word that signals exploitation.