I thought Bhutan was the happiest country! But the one thing I do know about Finland is that kids start school at 7 (if that’s true still) and that they are given no homework ever because it’s considered that kids need time to play. Happy children make for happy families. I suspect there is also social support like universal healthcare, etc.
Here’s a fun Finnish fact. Finland did their best to protect their Jews from the Nazis. They evacuated many to Sweden. A few were extradited under protest.