Many children suffering from speech sound disorders cannot pronounce the sibilant consonants correctly. We have developed a serious game that is controlled by the children’s voices in real time and that allows children to practice the European Portuguese sibilant consonants. For this, the game uses a sibilant consonant classifier. Since the game does not require any type of adult supervision, children can practice the production of these sounds more often, which may lead to faster improvements of their speech. Recently, the use of deep neural networks has given considerable improvements in classification for a variety of use cases, from image classification to speech and language processing. Here we propose to use deep convolutional neural networks to classify sibilant phonemes of European Portuguese in our serious game for speech and language therapy. We compared the performance of several different artificial neural networks that used Mel frequency cepstral coefficients or log Mel filterbanks. Our best deep learning model achieves classification scores of $$95.48\%$$ using a 2D convolutional model with log Mel filterbanks as input features.