This book is actually aimed at Middle-schoolers (I had to look that up, and seems to be roughly 10-13yo), so slightly younger than any of the books I usually read.
The blurb says:
An invisible girl. A missing mage. A world in need…
Brinley has spent most of her life lost in her own imagination, teaching bullfrogs to do gymnastics and pretending to be invisible. Now, when a magic bell from another world summons her across time and space on a journey to find her mother, she will discover real friendship, face true evil, and overcome her greatest fears in order to save the ones she loves.
The Mage and the Magpie is the first book in Austin J. Bailey's Magemother series: an epic middle-grade fantasy adventure series with witches, shapeshifters, and cliffhangers, and awesome kids (There are no boring adults in this book!).
I could tell this book was aimed at children - slightly quicker pace with less description and depth than I'm used to, but actually it was still really enjoyable. I'm not going to read the subsequent books in the series, but if my children were looking for a fantasy book I would encourage them to read this and I would buy the following books for them. (And admittedly, once I've bought them, for the kids, I probably would end up reading them.)
The book is really well written and the story is easy to follow, even though you are following multiple characters at times. I like books with a sense of good prevailing over evil, and even though there are sad bits, the book is built up as an adventure and you cannot always predict what will happen next.