Free social studies/history curriculum

My son is a first grader. For kindergarten we did math with confidence and logic of English an and b with some good and the beautiful science. This year I want to start some social studies but because he’s little and we’ve invested a lot in other subjects I’m curious if there are some loved free ones. Core knowledge? Easy peasy? I don’t want to create my own. I’m a check list and script person 🙃