This study aims to examine the change in intentions and views about the integration, mathematics teaching self-efficacy, and mathematical literacy self-efficacy after an online education about mathematics and children's literature to pre-service pre-school, primary school, and elementary mathematics teachers. The research participants consisted of fifty-four pre-service teachers who were selected by convenient sampling. A weak experimental pre-test and post-test design without control group was used. The data collection tools were the belief scale for the integration of mathematics, and children's literature, mathematics teaching self-efficacy belief, mathematics literacy self-efficacy scales and an open-ended question. The study findings revealed that the training enabled the pre-service teachers to gain positive inputs within the context of all the variables. Besides, the pre-service teachers' scores varied across their branches. A significant difference was identified between pre-service elementary mathematics teachers, and primary school and pre-school teachers in terms of the difference scores on intentions about integration. There are statistical differences between mathematics teaching self-efficacy and mathematical literacy self-efficacy pre-test and post-test scores. For further studies, various studies such as face-to-face, experimental studies on a single branch basis, may be conducted to examine the changes in beliefs and competences of pre-service teachers about mathematics and children's literature integration. [This study's initial findings were presented at the 5th International Turkish Computer & Mathematics Education Symposium (October 28-30, 2021).]