Background: Maternal input plays an important role in influencing linguistic development during the first years of life, and it is evident that mothers adapt their language according to their child's characteristics. Recently, it was demonstrated that maternal input addressed to children with sex chromosome trisomies (SCTs) at 8 months of age is prosodically and functionally different from that addressed to typically developing (TD) peers. Aims: The study aimed at analysing maternal input at 24 months when the presence of a language delay could be more evident than during the preverbal stage. We were interested in examining if maternal input was influenced by a diagnosis of SCT (by comparing children with SCT and TD children) or by children's linguistic level (by comparing children with weak lexical ability versus children with typical lexical ability regardless of the presence of genetic diagnosis). Methods and Procedures: Forty-four mother--child dyads in which the children had an SCT and 20 mother--child dyads in which the children were TD participated in the study. Of these 64 dyads, 23 children (21 with SCTs and two TD children) formed the group of children with weak lexical ability (children with a vocabulary size lower than 50 words at 24 months). Maternal utterances were collected during one video-recorded play session and were then coded considering both the linguistic and functional features of the input. Outcomes and Results: The results showed that the input addressed to 24-month-old children with SCTs is as rich and complex as that addressed to TD peers. Moreover, no significant differences in the functions expressed by maternal input were found (all ps > 0.05). Comparing the children with weak lexical ability and the children with typical lexical ability in our sample, having a poor vocabulary at 24 months of age showed a significant influence on the maternal input features: the input addressed to children with weak lexical ability was characterised by a higher presence of attention getters (U = 217.00, p = 0.007) and a lower proportion of questions (U = 236.00, p = 0.017) than that of mothers of typically-talking children. Conclusions and Implications: At 24 months of age, it seems that the presence of a language delay and not belonging to the clinical group of children with SCTs influences the functional characteristics of the maternal input. It is important to support the parents of children with SCTs during the communication process and later during their child's development, leading them to observe their children's manifested skills rather than looking for possible predicted difficulties.