A man throws his young boy playfully into the air standing on a beach.
A Dad and son is playing on the beach.
The fact that a man is throwing 'his' young boy into the air indicates that they are father and son, so this has been rephrased as Dad and son. Also throwing him playfully into the air can be rephrased more simply as 'playing'.
The man throws "his young boy", which shows that the relationship between man and boy is that of Dad and son. The word "playfully" suggests that the two are playing.
a man is the dad and young boy is his son