The direction of health development currently emphasizes promotive and preventive efforts without leaving out curative and rehabilitative aspects. Every child has the right to obtain basic immunization in accordance with the provisions. Immunization is carried out to prevent the occurrence of diseases that can be prevented by immunization. UNICEF supports government efforts to restore children's access to essential health services and to address the decline in routine immunization rates. The COVID-19 pandemic is the main cause of the decline in child immunization in Indonesia, causing supply chain disruptions and reducing the availability of health workers. This study used an analytic survey method with a cross-sectional approach. The number of samples in the study was 62. The research instrument used in collecting data was a questionnaire sheet. The results showed that out of 62 respondents with good knowledge and booster immunization, as many as 50 respondents (91%) did not do booster immunization, as many as 5 respondents (9%). Respondents with poor knowledge but who immunized included as many as 5 respondents (71%), and those who did not do booster immunization were 2 respondents (29%). Maternal attitudes of 62 respondents who had a positive attitude toward booster immunization were 50 respondents (100%). Negative maternal attitudes about booster immunization but still perform booster immunization as many as 5 respondents (42%), and do not perform booster immunization as many as 7 respondents (58%). From the statistical test results obtained, there is a significant relationship between knowledge of booster immunization in toddlers (p value = 0.000) and maternal attitudes towards booster immunization in toddlers (p value = 0.000). Maternal knowledge is very important in providing booster immunization. Without good knowledge, the mother will not necessarily understand the importance of booster immunization. Likewise with attitude; if the mother's attitude is positive, it will be better for booster immunization status. One of the factors that influences maternal attitudes is personal experience. This personal experience can create strong assumptions and have a direct influence on one's attitude.