Young orphan Pip spends his time in cemeteries thinking about his dead baby brothers.
Pip is describing his reaction to the head stones of his family members in the cemetery. He was the only child of his parents who lived, but neither of them did so he lives with his sister. He describes his dead baby siblings as “five little stone lozenges” his dead brothers “who gave up trying to get a living exceedingly early in that universal struggle” (ch 1, p. 4). Pip has a vivid immigration, and he is imagining his brothers being born dead.
I am indebted for a belief I religiously entertained that they had all been born on their backs with their hands in their trousers-pockets, and had never taken them out in this state of existence. (ch 1, p. 4)
Pip imagines the family members he never met from their headstones. His parents begin to look like their tombstones in his imagination, and so do his baby brothers.
It should be noted that the five little tombstones actually do exist, and they are in a cemetery in Rochester, in Kent, England where Dickens grew up. Clearly they caught his imagination as well as Pip's.