son. The Hebrew accent (Dechi) emphasizes this word to show (1) his own early training (Pro_4:3); (2) those whom he would instruct (verses: Pro_4:1, Pro_4:2); (3) his instruction (verses: Pro_4:5-9.)
only beloved = unique.
in the sight of my mother. A special various reading, called Sevir (App-34), reads "of my mother's sons". So in some codices, with several early printed editions.