I wouldn't worry about social studies in Kindergarten. At this age they are building the foundation for later on and a lot of it is stuff your child probably just naturally knows. I live in Texas so I looked up the TAKS requirements for Kindergarten and there really is no set curriculum but more a building block for later on. Such as holidays:
History. The student understands that holidays are celebrations of special events. The student is expected to:
(A) explain the reasons for national patriotic holidays such as Presidents' Day and Independence Day; and
(B) identify customs associated with national patriotic holidays such as parades and fireworks on Independence Day.
I would say look up your states standardized criteria for Kindergarten and look through it. If there is any specifics you can add that in for extra work but the building blocks your child will probably naturally understand that and it won't be much of a transition for him/her.
What I mean by the building blocks is stuff like this:
History. The student understands the concept of chronology. The student is expected to:
(A) place events in chronological order; and
(B) use vocabulary related to time and chronology, including before, after, next, first, and last.
Chances are he/she already understands this and even more so naturally does it. I know my 2 yr old already does it and has for a very long time. It really is an interesting read.
I hope that helps.
