Speaking is a fundamental way of communication, developed at a young age. Unfortunately, some children with speech sound disorder struggle to acquire this skill, hindering their ability to communicate efficiently. Speech therapies, which could aid these children in speech acquisition, greatly rely on speech practice trials and accurate feedback about their pronunciations. To enable home therapy and lessen the burden on speech-language pathologists, we need a highly accurate and automatic way of assessing the quality of speech uttered by young children. Our work focuses on exploring the applicability of state-of-the-art self-supervised, deep acoustic models, mainly wav2vec2, for this task. The empirical results highlight that these self-supervised models are superior to traditional approaches and close the gap between machine and human performance.