I read this poem to myself a few times, and, as I did, I heard a very nostalgic and wistful tone in the speaker's voice. I actually felt kind of bad for him. I think we all know what it's like to wish we could still be little kids again and get away with pretty much anything, and that's the point that I thought Heaney was making in his poem.
Throughout the poem, I noticed that there are references to reflections in almost every stanza: the lack of one due to the depth of the first well, the white face at the bottom of the second well, the rat slapping across his reflection in the third well, the reference to Narcissus, and the way he parallels his reflection in the wells to his reflection in his writing. The fact that he created the parallel changed the entire meaning of the poem for me. Also, his reference to the River Helicon in the title indicate that there is another, negative parallel with the river to, I assume, the wells. This made me wonder whether he was really ashamed of his connection with the wells and his childhood memories.
The first stanza tells us what the speaker enjoyed as a child: wells and old pumps, and all the messy things that came with them. This establishes the feeling of nostalgia in the poem. The second and third stanza describe two wells in particular which must have been important enough to catch in his memory. The first well, in a brickyard covered with rotting boards, was deep enough that he could not see his reflection, but apparently could still hear the water at the bottom. I thought this symbolized the mysteries we find as children, which are so fascinating to us. The second well was shallow and overgrown, so that he could pull out roots from the bottom. This seemed like the impelling curiosity which pushes children to discover the truths behind the things they don't understand.
"Now to pry into roots, to finger slime, To stare, big-eyed Narcissus, into some spring is beneath all adult dignity. I rhyme to see myself, to set the darkness echoing" This last stanza seemed to hold a lot of meaning. Everything he had done in his childhood, everything that had made him happy and had been the essence of his innocent mind had been taken from him in his adulthood. He is forced to substitute a more mature activity, writing, for his childish adventures in order to fill the void within himself and to keep from losing his unique, inner spirit. It seems like a sad little story to me, but whether or not we like it, growing up is something we all have to accept eventually...to an extent.