In this paper, we examine the relationship between participants' childhood science, technology, engineering, and mathematics (STEM) related experiences, their STEM identity (i.e., seeing oneself as a STEM person), and their college career intentions. Whereas some evidence supports the importance of childhood (i.e., K-4) informal STEM education experiences, like participating in science camps, existing research does not adequately address their relationship to STEM career intention later in life. Grounding our work in identity research, we tested the predictive power of STEM identity on career intention (N = 15,847). We found that for every one-point higher on our STEM identity scale, participants' odds of choosing a STEM career in college increased by 85%. We then tested whether a variety of childhood informal experiences predicted participants' STEM identity. While controlling for home environment, gender, and other relevant factors, only talking with friends and family about science, and consuming science and science-fiction media (i.e., books and television) were predictive of STEM identity in college.