Being the Gabbai Tzedakah is a Mitzvah. And we all hope they kinderlach will be a Talmid Chochom. That’s what they’re going to Yeshiva for.
you still didn’t mention which mitzvah it is (are there 614 mitzvos in the torah) we can hope, but until they are talmidei chachamim they can’t be gabbai tzedakahs