Early guidance emphasizes the provision of information to families about growth and normal development in childhood such as specific information about security at home. This research aimed to analyze mothers' knowledge about the prevention of accidents in childhood before and after an educational intervention. It was conducted as a quasi-experimental study with 155 mothers in a Basic Health Unit in northeastern of Brazil in April and May of 2015. The data were collected in two stages through a self-report questionnaire performed before and after the educational intervention by the subjects. The results revealed a significant increase in knowledge about prevention of accidents in childhood in all the self-applied questions (p<0.05). After the educational intervention, there seemed to be a significant difference with the questions regarding the knowledge on preventing fall (p=0.000), drowning (p=0.000), and intoxication (p=0.007). The authors concluded that the educational intervention performed in this study increased the subjects’ knowledge on prevention of accidents in childhood.