Gentle alliteration is used throughout "Eden Rock." For example, note in the /t/ sounds of lines 3 and 4 (the same sound is used as consonance here too). They seem to serve two functions. The first of these is to make the lines sound carefully constructed, as though the speaker is making a deliberate and concerted effort to create a faithful image of his father. As a delicate sound too, the /t/ alliteration also seems to bring the image of the small "trembling" dog to life:
... Tweed, his terrier Jack
Still two years old and trembling ...
The speaker uses alliteration when describing his mother as well, the repeated /d/ and /r/ sounds in "dress," "drawn," "ribbon," and "straw" again making the description sound careful and precise.
Another evocative moment of alliteration occurs in line 8:
Her hair, the colour of wheat ...
These two /h/ sounds demand an exhalation of breath when read aloud, which conjures up the sound of wind to emphasize the outdoor setting described in this stanza.
There is also alliteration across lines 11 and 12 through the repeated /p/ and /s/ sounds in "paper," "slowly," "sets," "same," "plates," and "painted." Aside from having a similar effect to some of the earlier alliteration—the sound of careful poetic construction conveying the way that the speaker's memory/vision of his parents is carefully put together—it's particularly notable that there are three words that begin with /p/ sounds. This subtly supports the image of the family unit—the trio of son, mother and father—and anticipates the "three suns" of line 13.
Line 17's use of alliteration is again highly significant. The speaker describes his parents "beckon[ing]" to him "from the other bank," seemingly reassuring him that they will be there to meet him when he dies ("crosses"). The two /b/ sounds chime with one another from either end of the line, representing the physical and metaphorical divide between the speaker and his parents, and between life and death.