The oral problems of young children are particularly serious because they are at a critical moment in developing good oral hygiene habits. How to help them maintain oral cleaning through sensors and artificial intelligence technology has become a research point of intelligent Internet of Things. We present an easy accessible monitoring system for evaluating the tooth brushing with smart devices. The system captures the users’ brushing behaviors (e.g., the motion of hands and the acoustic signals during tooth brushing) through the two build-in sensors. Then the collected data is transmitted to the smartphones and evaluated through a designed machine learning-based model. Finally, a DNN model is adopted to significantly improve the accuracy of detecting tooth brush tasks by up to 97.7%.