Hello Jakob and Kathleen !
I just happened to find this crazy website today and it feels nice to read my own family name there ! We are quite a big family and we do originate from the "Zaanstreek" in the North of Holland. My grandma says "Kaar" is an old word or a dialect for "windmill", my dad says a "Kaar" is the basket where you keep the fish in after catching it. I would love to hear whatever you have found out about the name and history of the van het Kaar family ! Daag !