335D: Children’s Book About Climbing A Mountain

This was a book for younger children that I borrowed repeatedly from the library in the early 1970's in the UK. All I can remember are the first few lines:

“It wasn’t a cold day. It wasn’t a hot day. It was a day just right for climbing a mountain.”

I know it was a picture book, but I have no more idea about what happened in the story.

I’d love to track it down if possible.

322J: The Mountaineer Children (and Dog) (Solved!)

Title: The Mountaineers – A children’s book from the 40’s
I am not sure that this is the correct title, as I have been unable to find it though any searches.  However, the book had a wonderful illustration on the cover of a number of children and a large dog climbing a mountain or hill.
I don’t remember much about their adventures, but the book was re-printed in the 70’s with the same cover illustration.
Thanks.