This study examined the structure of children's mental lexicons through performance on 2 short experimental tasks, 1 in which children repeated familiar monosyllabic real words varying in neighborhood density and 1 in which they repeated CVC nonwords varying in phonotactic probability. Two groups of typically developing children with mean ages of 4;3 (years; months; n = 16) and 7;2 (n = 15) participated. In the group of younger children, offset-to-onset response latencies were not systematically affected by lexicality, phonotactic probability, or neighborhood density. Onset-to-onset latencies showed an effect of phonotactic probability on nonword repetition. Children in the older group repeated high-density real words with longer latencies than low-density real words. They also repeated high-probability nonwords with shorter latencies than low-probability nonwords. This was true for both the onset-to-onset andoffset-to-onset repetition latencies. Children in both age groups repeated vowels embedded in high-probability nonwords with shorter durations than vowels embedded in low-probability nonwords. These findings suggest that lexical competition and phonological facilitation emerge in development and that the rate of development is different for different dependent measures.