The current study investigates Spanish children's variation between the standard and non-standard forms for second person singular preterit --s ("caiste" [approximately equal to] "caístes"). All second person singular preterit forms were extracted from the spontaneous speech of 78 children in Spain and analyzed for the effects of age, language contact setting, and lexical frequency. Results show that children in contact with Galician and Catalan produce more non-standard than children in non-contact areas like Madrid. Meanwhile, low-frequency verbs (e.g., "pillaste") are more likely to occur with the non-standard --s than high-frequency verbs (e.g., "fuiste"). However, age is not a significant predictor of children's 2sg preterit production. These preliminary findings demonstrate that Spanish children do have the non-standard -s in their speech, and that their 2sg preterit forms are significantly conditioned by language contact and lexical frequency.