Background/Objectives: In 2022, the full-scale invasion in Ukraine forced over 6 million Ukrainians, primarily mothers and children, to seek safety outside of the country. This massive influx has posed a significant challenge to the Polish healthcare system, particularly regarding routine vaccination for children. This study aims to examine the vaccination intentions of displaced Ukrainian mothers, their compliance with the Polish National Immunisation Programme (PNIP), and the factors that influence these intentions. Methods: A web-based survey (June–July 2023) was conducted among Ukrainian mothers in Poland. The questionnaire assessed the importance placed on vaccination, knowledge of PNIP, and concerns related to displacement and vaccination. Hierarchical logistic regression identified key determinants. Results: Among 2572 respondents, 64.5% reported that their children had received only some or none of the recommended vaccines. Key barriers included unfamiliarity with PNIP, limited knowledge of vaccines, and concerns about vaccine side effects. Of mothers whose children had not followed PNIP, 41.7% intended to vaccinate, 33.1% refused, and 25.2% were undecided. Regression analysis identified perception of vaccination importance as the strongest predictor. Partial adherence to PNIP doubled vaccination likelihood, while a firm plan to return to Ukraine reduced it 2.4 times. Mistrust in vaccines increased refusal risk tenfold. The final model confirmed mothers’ attitudes towards vaccination and future plans (return to Ukraine) as dominant factors. Conclusions: This study underscores the complex determinants shaping vaccination decisions in conflict-displaced communities. It provides insights for public health strategies to enhance vaccine uptake by reducing access barriers, restoring trust, and strengthening vaccine literacy.