Introduction: This paper investigates techniques used by children in year 4 (age eight to nine) of a UK primary school to reformulate their queries, and how they use information retrieval systems to support query reformulation. Method: An in-depth study analysing the interactions of twelve children carrying out search tasks in a primary school lesson; including observations, search recordings, post-task interviews and teacher interview. Analysis. The search screen recordings were analysed for task performance. The queries were categorised using both Broder's taxonomy (2002) and query reformulation type schemes. The interviews and observations were analysed inductively using thematic analysis. Results: Children reformulated queries by switching information retrieval system, extracting information from search results, and by using "did you mean" and auto-complete functionality. The children also reformulated queries by using previous queries, correcting errors, and making their queries more specific. The type of query reformulation support the children used varied according to the type of query entered, with children submitting both question queries and broad-based topic queries. Conclusions: The children mostly reformulated queries based on their interactions with information retrieval systems, rather than their prior knowledge. Search systems could further support children by (1) tailoring tools to the type of query (question or broad-based) entered, (2) making suggestions for the narrowing of queries as the children found this particularly difficult (3) accommodating children's linear scanning of search results as this led to unnecessary query reformulations. [This paper was published in: "Proceedings of ISIC: The Behaviour Conference" (Leeds, England, Sep 2-5, 2014), Part 2, Paper isic31.]