Coming-of-age/portal sci-fi book about a teenage girl and her younger brother, who are transported to another realm and have to complete a quest [duplicate]

Question

Definitely a long shot, but I remember reading this book in the late '80s or early '90s.

It was about a teenage girl and her younger, early-teens brother, and they somehow got transported to another realm. In this realm they have to complete a quest, and maybe she has magic powers now (?). I seem to remember the brother picking up ground fighting and/or sword skills as this quest unfolds.

And the only part I can remember is how it suddenly occurs to her (much later in the book) how much her brother has changed, that he's grown taller and his jeans and shoes don't fit anymore, and he's shed his babyfat and has basically sprouted into a young man during this quest.

It may have been published in the 1980s. I would give my kingdom to find this book again. LOL Thank you!

Answer 1

This might be The Wizard Children of Finn by Mary Tannen as per 80s book similar to Narnia but with a more Celt feel, allusions to Finn MacCool and eating "the salmon of wisdom".

Fiona McCool, a wise-cracking eleven-year-old, and her dreamy thumb-sucking brother, Bran, are lured into the woods by a mysterious whistle. The whilstler turns out to be Finn, an enchanted boy who has been watching the McCools, hoping to make friends with them. Fiona and Bran are caught up with him in a magical spell that flings them back through time to Finn's homeland, the Ireland of two thousand years ago. They journey on foot across ancient Ireland -- over two rivers, battling wild beasts, traveling toward the awesome celebration of Samhain, where their fate is to be decided. Fiona becomes Finn's poet, spinning their adventures into poems, while Bran remembers the tales perfectly and recites them. Together, the McCools document the story of Finn, a boy on the brink of manhood whom they grow to love, but cannot begin to understand.

Near the end of the book does have Fiona realizing that Bran has shed much of his baby fat.

Bran stood before the fire. With everyone sitting down, he looked much taller than he really was. Hiking through the woods for a couple of weeks had gotten rid of the baby fat. His face was harder, more boy like.

She doesn't have magic powers in the first book, but picks up a few in the sequel, which also has her realizing that

her mother previously traveled to this world, and Finn is her father.