Early childhood caries (ECC) is reported to be the most prevalent childhood disease. It is a chronic, infectious dental disease affecting children aged between birth and 71 months. Untreated ECC can lead to toothache, swelling, abscess, immature loss of primary teeth, and thereby, significant impacts on children's physical and emotional status. Nowadays, ECC has been recognised as a serious public health problem in developing as well as developed countries. Although ECC has a complex aetiology, existing evidence reveals that tooth brushing, appropriate eating habits, and regular dental check-ups are effective in preventing the development of ECC.

In this study, oral health education will be reinforced by a series of visual education materials (social stories or conventional leaflets), which covering the three topics in ECC prevention, namely "tooth brushing", "healthy diets", and "dental visit". Sample size calculation is performed by the program G\* power 3.1.9.2. The primary outcome is the development of new dental caries over the 24-month study period. Clinical oral examinations will be performed according to the following criteria: i) Caries experiences were assessed by the International Caries Detection and Assessment System(ICDAS); ii) Oral hygiene status by Simplified oral hygiene index of Greene and Vermilion (OHI-S); iii) gingival health status by Modified Gingival Index of Lobene (MGI). Dental examination will be performed at Special Child Care Centres by a paediatric dentist with a disposable mouth-mirror attached to an LED light. Tell- Show-Do (TSD) technique will be used to improve children's cooperation level. Tooth-brushing performance will be assessed by two observers. After dental examination and tooth-brushing assessment, a standard hands-on tooth-brushing training will be provided immediately to each child and his/her parent. Oral health instruction will also be illustrated to the participants, reinforced by social stories (experiment group) or conventional leaflets (control group). Questionnaires regarding children's oral health related behaviours and family demographic information will be completed by parents, while children's developmental profile will be assessed by staff in Special Child Care Centres. Children' oral health status and expected behaviours (tooth brushing, healthy eating habits and dental-visit experience) will be assessed at 6-month, 12-month and 24-month intervals.

All the data will be analysed using IBM SPSS. Continuous valuables such as dmft, dmfs, S-OHI, MGI scores between the control and test groups will be analysed by two-sample t test, paired-t test, Mann-Whitney Test when appropriate. Chi-square statistics will be used to assess the differences in categorical variables between control group and test group, such as caries incidence, tooth-brushing frequencies, snacking frequencies, and dental-visit frequencies. McNemar's test will be used to analyse whether children's oral-health related behaviours will be changed before and after intervention. Regression analyses will be conducted to determine potential factors associated with children's oral health status or oral-health related behaviours in the model. The significance levels will be set to be P \< 0.05.