Systematic review of the literature on characteristics of late-talking toddlers.

BACKGROUND Research has investigated late-talking toddlers because they are at great risk of continuing to experience language-learning difficulties once they enter school and hence are candidates for early intervention. It is also important to consider this group of children with regards to the immediate characteristics which are detrimental to their development and for which early intervention has become increasingly available. AIMS To review the literature on late-talking toddlers in order to identify the characteristics of this population whose importance has been clearly demonstrated, identify sources of incongruence in findings, and to underscore aspects of language delay at 2 years of age and characteristics about which additional knowledge is needed. MAIN CONTRIBUTION The review highlights the need to define the language difficulties found in late-talking toddlers based on clinical profiles that go beyond the criterion of an expressive vocabulary delay. It also underscores the association between vocabulary delay and characteristics of the child such as social-emotional development and characteristics of the socio-familial environment such as language stimulation. CONCLUSIONS Future research should take into account the lack of homogeneity observed within the population of children with a vocabulary delay at 2 years of age and attempt to identify subgroups within late-talking toddlers. It should also consider a multifactorial perspective of child development to further the understanding of this phenomenon.