Existing studies are inconclusive about if and how children's stronger language can support target language instruction. This study analyzed 29 Malay language teachers' switching practices, reasons for switching, and perceptions of their Malay-English bilingual children's language preferences and needs, in Singaporean preschool classrooms. 5 teachers' and 68 children's actual language practices were video-recorded, transcribed and coded for frequency and reasons for codeswitching. The Computerized Language Analysis (CLAN) software calculated these occurrences, and the combos function was used to examine the impact of teachers' language on children's classroom language output. The results revealed mismatches between teachers' reported and observed language perceptions and practices. Language separation ideology is prevalent in Singapore, yet only one teacher claimed to never use English. All teachers were observed to switch to English at varied frequencies. While most Malay language teachers reported that their English use was because of instructional purposes, they were observed codeswitching mainly due to habitual reasons. These findings reflect the need to address gaps between perceptions and practices in preschool language instruction, and to consider further steps in preparing teachers to address the reality of language needs and practices in their classrooms.