Aim There has been an increase in consultations related to eating and oral function of children, such as not chewing food properly and swallow without chewing; however, there have been few studies about oral function evaluation. We have devised a mouth rinsing function test (MRFT) to evaluate the oral function of children by grading mouth rinsing function into five stages. We aimed to investigate the effectiveness of MRFT for evaluating the oral function of children and to investigate factors relating to the MRFT scores. Methods The participants were 182 children (age 3–6 years; 98 boys and 84 girls) attending nursery school, who underwent an oral examination and evaluation of MRFT and occlusal force. Data on growth history and eating behavior were collected from parents through a questionnaire. Results The MRFT score significantly correlated with age and if breastfeeding or bottle-feeding was stopped earlier. Children whose parents worried about their eating habits tended to have lower MRFT scores. There was no significant correlation with occlusal force or the thickness and length of the masseter. Conclusions MRFT is effective for evaluating the oral function of children because the MRFT score increases with age. The MRFT score is related to eating behavior; hence, children with low MRFT scores should be supported appropriately. MRFT was not correlated with occlusal force or the thickness and length of the masseter muscle; therefore, it is necessary to examine the oral dexterity, using MRFT, when evaluating the oral function of children.