Elspeth started out as... 8ish, I want to say? But maybe she was a bit older than that. Anyway, she's adult in later books when Selenay is still around, even if she spends much of that time away from home.
I would also suggest:
In Diane Duane's Young Wizards books, Nita Callahan's parents are both significant supporting characters for the first few. Then her mother dies (of cancer), but she's a significant character throughout that and in memory later.
Robin McKinley's Spindle's End. Okay, the characters would refer to themselves as godmothers, IIRC, and are careful not to claim the place of Rosie's birth mother (since they're raising her in hiding to protect her), but... they raise her from infancy to a teenager. They're her adoptive mothers in every way that matters, really.
no subject
I would also suggest:
In Diane Duane's Young Wizards books, Nita Callahan's parents are both significant supporting characters for the first few. Then her mother dies (of cancer), but she's a significant character throughout that and in memory later.
Robin McKinley's Spindle's End. Okay, the characters would refer to themselves as godmothers, IIRC, and are careful not to claim the place of Rosie's birth mother (since they're raising her in hiding to protect her), but... they raise her from infancy to a teenager. They're her adoptive mothers in every way that matters, really.