Background: Tooth wear has a multifactorial etiology, thus it should be assessed within a multiple-variable framework. The objective of this investigation was to assess the association of dietary habits and parental-reported sleep tooth grinding (STG) with tooth wear in children with mixed dentition. Methods: One hundred twenty-one (N = 121) subjects (mean age 9.6 years) participated in a cross-sectional study. Wear of 1637 teeth was evaluated using the screening module of the Tooth Wear Evaluation System (TWES). Parental-report of STG was evaluated by means of the Children's Sleep Habits Questionnaire (CSHQ), whilst dietary habits were investigated by means of the Health Behaviour in School-Aged Children Food-Frequency Questionnaire (HBSC-FFQ). Data were analyzed with the Spearman correlation test and ordinal-multiple-variable regression analyses. Odds Ratio (OR) and ordinal OR were obtained for the independent variables included in the models. Results: Parental-report of STG is not associated with tooth wear in the mixed dentition; some dietary habits were found to be correlated with specific tooth wear patterns, but the correlation values were weak. Associations were found between dietary habits and the increase-to-increase severity of occlusal/incisal and non-occlusal/non-incisal tooth wear of some teeth (OR > 2). Conclusions: A strong correlation of dietary habits and sleep tooth grinding with tooth wear in the mixed dentition was not demonstrated. However, dietary habits showed to have effects in terms of increase-to-increase severity.