"Sisters and brothers, little Maid, How many may you be?" "How many? Seven in all," she said, And wondering looked at me.
"And where are they? I pray you tell." She answered, "Seven are we; And two of us at Conway dwell, And two are gone to sea.
"Two of us in the church-yard lie, My sister and my brother; And, in the church-yard cottage, I Dwell near them with my mother." (13-24)
At the beginning of the poem, the speaker and child have a pretty typical convo about family. He asks how many siblings she has, and she says "seven are we." In this seven, she includes herself, her siblings who are in Conway and off at sea, and also her brother and sister who are dead. That sounds reasonable to us.
"Their graves are green, they may be seen," The little Maid replied, "Twelve steps or more from my mother's door, And they are side by side.
"My stockings there I often knit, My kerchief there I hem; And there upon the ground I sit, And sing a song to them.
"And often after sun-set, Sir, When it is light and fair, I take my little porringer, And eat my supper there. (37-48)
Here, the little girl explains how much her dead siblings do count in her life. In fact, she spends a whole bunch of time hanging out at their graves, singing them songs, eating her supper with them. These siblings may be dead, but they are still very much a part of the girl's family.
"The first that died was sister Jane; In bed she moaning lay, Till God released her of her pain; And then she went away.
"So in the church-yard she was laid; And, when the grass was dry, Together round her grave we played, My brother John and I.
"And when the ground was white with snow, And I could run and slide, My brother John was forced to go, And he lies by her side." (49-60)
In these stanzas we get some specifics about the death of the girl's siblings, Jane and John. Their deaths sound pretty tragic to us. These kids are very much on the girl's mind, which, for her, is enough for them to still count—or matter—in her life.
"How many are you, then," said I, "If they two are in heaven?" Quick was the little Maid's reply, "O Master! we are seven."
"But they are dead; those two are dead! Their spirits are in heaven!" 'Twas throwing words away; for still The little Maid would have her will, And said, "Nay, we are seven!" (61- 69)
The speaker will not give in. He just doesn't agree with the girl. But she stands firm. She will not give in, either. For her, once family, always family. The last line of the poem is her emphatic exclamation: "Nay, we are seven!" Once seven, always seven.