An inadequate level of oral health literacy (OHL) can hinder the understanding of dental information, which can have a negative impact on health promotion actions, such as the rational use of fluoride. The aims of the present study were (1) to look for association between parents/guardians’ OHL and the amount of fluoride toothpaste used for children from zero to four years of age; (2) to compare the effect of different modes of educational interventions on the amount of fluoride toothpaste used for children from zero to four years of age; and (3) to assess the ability of parents/guardians to choose a toothpaste with adequate fluoride concentration, after the educational intervention. A randomized intervention study was conducted with parents/guardians of children from zero to four years of age (<i>n</i> = 145). The participants answered the Oral Health Literacy Adults Questionnaire and a questionnaire addressing sociodemographic characteristics. The participants were allocated to four intervention groups based on type of counseling (written, oral, written + photograph, and oral + photograph), with randomization stratified by level of OHL. The participants were instructed to place the adequate amount of toothpaste on a toothbrush for children from zero to four years of age (smear of 0.125 mg) before and after the intervention. The correct choice of toothpaste was also evaluated by the interpretation of the labels of four toothpastes of different brands and with different concentrations of fluoride. Associations between variables were tested using the Student’s <i>t</i> test and one-way ANOVA. Level of OHL was associated with the amount of fluoride toothpaste deposited prior to the educational intervention (<i>p</i> = 0.021) and the percentage of approximation to the appropriate amount of fluoride toothpaste (<i>p</i> &#x3c; 0.05). The choice of toothpaste was associated with schooling (<i>p</i> = 0.031). In conclusion, parents/guardians with adequate OHL better quantified fluoride toothpaste before and after the educational intervention and also came closer to the appropriate amount of toothpaste after the educational intervention. No significant differences in the final amount of toothpaste placed on the toothbrush were found among the intervention groups. The choice of the correct toothpaste was associated with a higher level of schooling.