The aim of this longitudinal study, carried out on a sample of Slovenian-speaking toddlers, was to analyze developmental changes and stability in early vocabulary development; to establish relations between toddler's vocabulary and grammar; and to analyze the effects of parental education and the frequency of shared reading on toddlers' vocabulary and grammar. The sample included fifty-one toddlers, aged 1;4 at the time of the first, and 2;7 at the time of the last, assessment. Toddlers' vocabulary and grammar were assessed six times during a 15-month period using the Slovenian adaptation of the CDI. Our findings suggest great individual differences in both size and rate of toddlers' vocabulary development. Toddlers' vocabulary scores remained relatively stable across a 3-month period. Early vocabulary at 1;7 predicted vocabulary, sentence complexity, and mean length of utterance (MLU) at 2;7, while the frequency of shared reading mediated the effect of parental education on toddlers' vocabulary and grammar at 2;7.