The second stanza takes us back to the simpler, magical time of childhood.  "She was a child and I was a child, /     In this kingdom by the sea,"  the speaker recalls.  Note the italicized emphasis here.  The speaker fondly recalls a time when they were both able to be mentally "together." 

The speaker savors these magical moments, fondly recalling a world in which myths were real and love loyal.  The stanza continues:  "But we loved with a love that was more than love— / I and my Annabel Lee— / With a love that the wingéd seraphs of Heaven / coveted her and me."  In this final phrase, the love the two shared was so magical and deep that even the creatures of hevean were jealous. 

Annabel, however, grows up and out of their fantasy land.  Stanza three reads:

And this was the reason that, long ago,
    In this kingdom by the sea,
A wind blew out of a cloud by night
    Chilling my Annabel Lee;
So that her high-born kinsmen came
    And bore her away from me,
To shut her up in a sepulchre
    In this kingdom by the sea.

The effect is to produce the vision of a man who himself refuses to grow up, and is forever doomed to mourn the ephermal nature of childhood.