My DD6 has a thing with dates, but not the same way that you are describing. She likes to know everyones birthday. Started when she desided it was time she learned the months of the year (she was almost 3) She would look at the calendar starting with January and ask "who has a birthday in January?" and would go through all the months and then do it over again, and over again. She still knows everyones birthday and it's really nice because she reminds me when one of my in-laws birthdays are coming up.
