Frequency of occurrence in the input is a main factor determining the ease of acquisition in first language learners. However, little is known about the factors relevant for the acquisition of low-frequency items. We examine the use of aspectual markers in a longitudinal corpus of Chintang (Sino-Tibetan, Nepal) children (ages 2;1-4;5). Only 7.7% of all Chintang verbs are overtly marked for aspect. Chintang has three aspect markers, one of which is substantially more frequent than the others. One of the low-frequency markers is positionally and prosodically more salient, appearing at the word-boundary. Using a Bayesian beta-binomial model, we assess the distribution and flexibility of use of aspectual markers in the input and children's production. Our analysis shows that the most frequent marker was acquired earliest, as predicted. For the low-frequency markers, position, segmentability and uniformity are better predictors of ease of acquisition.

The initial phase of linguistic production by children is char-acterized by rote-learned, lexically restricted forms and con-structions. Only during later phases of language acquisitiondo they develop flexibility across a paradigm and mix lexicaland grammatical material more freely. In the development ofverb morphology, a correlation between the use of tense andaspect has been observed in many languages. It has been sug-gested that this leads to an intermediary state of paradigm cat-egorization based on temporal categories. So far the flexibilityof individual verbs occurring in different tense-aspect combi-nations has not been examined in detail. Here we evaluate theflexibility of verb use in a large longitudinal corpus of 4 Rus-sian children. We compute the Shannon entropy of verb stemsdistributed over individual grammatical forms. Results showthat children do not pass through a stage of paradigm cate-gorization based on aspecto-temporal categories. After a briefitem-specific phase of rote learned forms, they quickly becomeflexible users of verbs in both aspects.

Learning to understand and use agreement is an integral part of children's linguistic development. In Romance languages, this includes gender and number agreement between the controller and attributive or predicative adjectives or participles. We examine the development of this category in a case where children's task is complicated by syncretisms, multiple paradigms, and unequal input distributions. Romansh Tuatschin (Romance, Indo-European, Switzerland) presents children with two distinct paradigms for attributive (masculine and feminine only) and predicative (masculine, feminine, and neuter/unmarked) contexts of adjective and participle use. The masculine form in predicative use is the same as the neuter form in attributive usage. Thus the masculine form in these two paradigms differs. This could be challenging for the language learner. The distribution of these forms is heavily skewed towards the \emph{neuter} in predicative contexts but balanced in attributives. Examining production errors in children between 2;0 and 4;3, we evaluate the effects of frequency and syncretism and find that error-rate is affected by skewed distributions and less affected by syncretisms. This demonstrates the strong effect of input distributions on first language acquisition.

Learning to establish joint reference is an important milestone of communicative and linguistic development. Pointing is one of the first entry points into this process, since gestures often precede verbal communication. During early development, as well as later language use, pointing and linguistic utterances interact in many ways, complementing each other. However, little is known about the development of this relationship during development. In this paper, we focus on the development of the co-occurrence of finger pointing and accompanying utterances in two different cultures: Russia and Chintang (Sino-Tibetan, Eastern Nepal). We show that despite the differences in environment, the development of finger pointing and accompanying language use show substantial similarities. Early on, a larger proportion of points is not accompanied by language. As the children's linguistic abilities develop, children first use language to specify what is being pointed at, and later elaborate on some aspect of the referent.

Despite considerable differences in the structures of the world's languages and child-rearing practices, children show remarkable cross-linguistic similarities in their early lexical development, including a preference for nouns. Here, we analyze children's early lexical production in naturalistic longitudinal corpora in a large-scale cross-linguistic comparison of 10 typologically highly diverse languages. We assess morphological complexity as a possible explanatory variable for children's higher noun-to-verb ratios and evaluate whether children's gradual increase in morphological productivity is correlated with their gradual decrease in noun-to-verb ratios towards the level found in their ambient language. We show that in languages with complex verb morphology, children exhibit a higher deviation in their noun-to-verb ratio compared to adults. This deviation gradually diminishes as they become more productive in the use of their target language. This effect holds across languages, despite their differences in morphological complexity.