Mokie and Bik in North America

Henry Holt and Company Books for Young Readers

This is quite a different book than the Australian one, in text as well as illustration. Here's the opening excerpt:
Mokie and Bik lived on a boat called Bullfrog. They lived in it, on it, all around it -- monkeying up ladders and down ropes, over the wheelhouse and across the cabin floor.

“Twins!” their mother shouted, because the lines of her Art jiggled and jarred when Mokie and Bik played bumpboats. “Get out from underfoot!”

So Bik bumped Mokie out the door -- splat! -- into nanny Ruby’s bucket as she was sploshing the deck.

“Twins!” shouted Ruby. “Get out from underfoot!”

So they sunned like seals on the wheelhouse roof for about twenty hours till Ruby finished sploshing.