Global vaccination efforts to control the COVID-19 pandemic may be impeded by vaccine hesitancy. Attitudes and vaccine literacy are important factors that reduce vaccine hesitancy. The role of attitudes and vaccine literacy of parents on COVID-19 vaccine intention for their children under five years was unknown.Objective: This study aimed to assess parents' characteristics, vaccine literacy, attitudes toward the COVID-19 vaccine, and vaccine intention/hesitancy and to determine factors influencing parents' vaccine intention for their children under five years of age. Methods: A cross-sectional study was conducted using an online self-administered questionnaire before the authorization of the COVID-19 vaccine for very young children in Thailand. The sample consisted of 455 parents with children under five years old. The online questionnaire included parents' sociodemographic data, vaccine literacy, attitudes toward COVID-19 vaccine, and vaccine intention to get their children vaccinated. Results: About 98% of the parents received their COVID-19 vaccination, whereas only 45.1% reported they would have their children under five years old get vaccinated. About 54.9% were either not sure or refused their child's COVID-19 vaccination. A multiple logistic regression model identified factors that increased the odds of parents' vaccine intention: parents aged > 35 years, attitudes on safety and efficacy of COVID-19 vaccine for children, advice about the COVID-19 vaccines from healthcare personnel, and the belief that COVID-19 vaccine is helpful for their children. Attitudes that COVID-19 vaccination in children could be fatal decreased parents' vaccine intention. Need for more information about the COVID-19 vaccine for children and concern about the vaccine's side effects were the most frequent reasons for vaccine hesitancy and refusal. Conclusion: Parents should be provided with accurate information from healthcare personnel and media sources about the safety and effectiveness of the COVID-19 vaccine for young children under five years of age to overcome their hesitancy.