ABANDONED. Children's fantasy - siblings discover they can shapeshift into seals

[Lauren]

I read this book around 2013-2016. I remember the cover had some sort of remote, rocky island on it with a dark storm going on, and the silhouettes of two or maybe three young children near the bottom. I've forgotten the names of the characters, but I remember they were siblings, and that they discovered they could shapeshift into seals. I remember that the boy discovered he could hold his breath for an unnaturally long time at a swim competition, where everyone commented on how he swam the entire length of the pool without surfacing for air. I loved this book a lot, but I unfortunately forgot the title.

[Audrey]

A Stranger Came Ashore by Mollie Hunter?
The Seal Children by Jackie Morris?

[Lauren]

Audrey wrote: "A Stranger Came Ashore by Mollie Hunter?
The Seal Children by Jackie Morris?"

Hmm, they aren't the book I'm looking for, but they do seem interesting. Thanks for replying though :)

[Rainbowheart]

Might want to check the Selkies list.

[Kris]

No response, moving to Abandoned folder.

Lauren (OP) last posted in the group in May 2020.