331L: War Kids Seek Treasure

The book I am trying to identify was written over 60 years ago, and it features a group of children ages five or so through 14, or thereabouts.  They have been sent to the country because of the Second World War, and they become convinced there is lost treasure in the vicinity.  The only scene I remember takes place in church.  The younger kids are shocked and scandalized during the service as the collection basket enters their pew.  The eldest, instead of putting a coin in, pulls one out!  This is their first real clue.  The coin turns out to be a genuine gold doubloon.  The eldest boy may have been named Emil.  Do you know which book this is?

249G: Treasure concealed in a barn

I read this book in the 90’s but do not know if it was published prior.

There is a young boy whom begrudgingly goes to a family members home (may be a grandparent although I do not recall this aspect specifically). I think it was for his summer vacation. There is a local legend of missing treasure, maybe it was stolen? Many people have looked for the treasure over the years, but of course the boy finds it in a barn. I think the barn was on the property where he had been staying for the summer.

The treasure had been melted down and molded/crafted into items commonly found in a barn and covered or painted to conceal it. I believe he chipped off some paint of a candle stick or something, and the wagon in the barn actually was made of gold and also painted or covered in disguise. I hope this is enough to figure this out, I really loved the book as a kid and now want to read it to my children.