This study investigated the code switching behavior of bilingual parents when speaking to their children, and the relationship between this code switching and children's vocabulary development. The speech of 18 bilingual Spanish-English parents was transcribed and analyzed, and the total Spanish-English vocabularies of their 18-24 month old children were calculated by parent report. All of the parents code switched at least once, and several parents code switched fairly often. Intra-sentential code switching occurred less often than inter-sentential code switching; however, only the former had a significant, positive relationship with vocabulary. Intra-sentential code switching also positively related to translation equivalents in children's vocabularies. Code switching, in general, did not seem to be harmful to children's lexical development. Other factors possibly contributing to the results, along with directions for future research, are discussed.