There are so many discussions in the archive, I would suggest searching first in 'Suche in allen Foren' on 'mit freundlichen Grüßen.'
'Kind regards' is a very cool, formalistic, stereotypical phrase, used mostly in business correspondence, perhaps especially in British English. It is not warm or friendly, so it would sound strange in personal correspondence from a family, such as a Christmas card or letter. (The word 'kind' is actually not even very polite, as it appears to boast that it was kind of you to bother to send your regards, which is condescending if you think about it.)
There is also absolutely no reason to capitalize 'the' in the name of a family, whether or not it begins a new line.
If you intend the letter to be friendly, there are better options.
Best wishes from the Schmidts
With our warmest wishes,
the Schmidt family
Lisa, Karl, Max, and Julia
We appreciate your business!
Schmidt Family Fine Foods