Early establishment of healthy oral health behaviours is important to reduce early childhood caries risk. Two-way social media applications can economically assist caregivers. To evaluate the effectiveness of a LINE™ messaging service (MS) on promoting good oral health behaviors in Thai children. One hundred and ninety caregiver-child dyads (children aged 6-36 months) who attended a university dental hospital and two other hospitals were randomly assigned to receive age-appropriate dental health education via MS or through traditional on-site visits. Infographic posters, video clips, and supportive messages were delivered weekly to the MS group. Parental oral health knowledge and children's oral health status and practice were assessed at baseline and 6-month follow-up. The MS group showed significantly better scores in feeding habits (p = .034) and toothbrushing practice (p = .007). Parental knowledge increased in both groups; however, knowledge increased significantly in the control group (p = .001). Both groups exhibited improvements in the debris score but not in caries progression. The caregivers rated both methods as high to the highest satisfaction. The MS yielded comparable outcomes to traditional dental visits in promoting oral health behaviours.