Various measures for identifying the onset of babbling have been proposed in the literature, but a formal definition of the exact procedure and a thorough validation of the sample size required for reliably establishing babbling onset is lacking. In this paper the reliability of five commonly used measures is assessed using a large longitudinal corpus of spontaneous speech from forty infants (age 0 ; 6-2 ; 0). In a first experiment it is shown that establishing the onset of babbling with reasonable (95%) confidence is impossible when the measures are computed only once, and when the number of vocalizations are not equal for all children at all ages. In addition, each measure requires a different minimal sample size. In the second experiment a robust procedure is proposed and formally defined that permits the identification of the onset of babbling with 95% confidence. The bootstrapping procedure involves extensive resampling and requires relatively few data.

Consonant inventories are commonly drawn to assess the phonological acquisition of toddlers. However, the spontaneous speech data that are analysed often vary substantially in size and composition. Consequently, comparisons between children and across studies are fundamentally hampered. This study aims to examine the effect of sample size on the resulting consonant inventories. A spontaneous speech corpus of 30 Dutch-speaking 2-year-olds was used. The results indicate that in order to construct and compare inventories reliably, they should be drawn from speech samples that are equally large. A new consonant inventory procedure is introduced. The implementation of this procedure demonstrates considerably less variation in inventory size across children and word positions than reported previously. This finding has important implications for clinical studies that constructed and compared inventories of typically and atypically developing children without normalizing the sample size.

The impact of input frequency (IF) and functional load (FL) of segments in the ambient language on the acquisition order of word-initial consonants is investigated. Several definitions of IF/FL are compared and implemented. The impact of IF/FL and their components are computed using a longitudinal corpus of interactions between thirty Dutch-speaking children (age range: 0 ; 6–2 ; 0) and their primary caretaker(s). The corpus study reveals significant correlations between IF/FL and acquisition order. The highest predictive values are found for the token frequency of segments, and for FL computed on minimally different word types in child-directed speech. Although IF and FL significantly correlate, they do have a different impact on the order of acquisition of word-initial consonants. When the impact of IF is partialed out, FL still has a significant correlation with acquisition order. The reverse is not true, suggesting that the acquisition of word-initial consonants is mainly influenced by their discriminating function.

Compiling syllable type inventories from children’s spontaneous speech is all but straightforward: so far studies vary considerably in their methodologies and consequently the selection of the speech samples differs. This paper shows that different methodologies for selecting a speech sample lead to substantial differences in syllable inventories. Two main sources for this variation are explored: differences in size and content of the speech samples. Both factors influence the results significantly and this questions the comparability of previous study results. An empirical procedure to investigate syllable type development is proposed to overcome such methodological problems, and this procedure is implemented to provide an initial empirically sound assessment of the acquisition of syllable types in Dutch speaking toddlers.

Consonant inventories are commonly used phonological measures for analysing spontaneous speech data of young children with a normal or disordered language development. However, a standard procedure is lacking. In this study, different consonant inventories are derived following the guidelines of various existing procedures. Consonant inventories have usually been drawn from speech samples varying substantially in size. The size of the consonant inventories, however, is strongly related to the amount of speech data analyzed. Therefore, speech samples of equal sizes across children and across observation sessions should be used, a requirement often neglected in language acquisition studies.