Both language input and output are important to child language learners' heritage language development. Nevertheless, existing studies mainly focus on language input, leaving the significance of language output underexplored. The current study assessed 201 kindergarteners' Mandarin skills (i.e., receptive vocabulary, receptive grammar, and verbal fluency) in Singapore, and investigated the influence of children's Mandarin experience, and specifically output, on these Mandarin skills. The results based on multilevel models reveal that children's Mandarin experience plays a crucial role in the three Mandarin skills, after controlling for children's gender, language aptitude, and English proficiency. Specifically, children's onset age of Mandarin speaking and the number of places where they used Mandarin alone significantly predict all the Mandarin skills.