Current research regarding Baby Sign and its effect on early language and communication development is inconclusive. This study investigated the effects of Baby Sign class attendance on early language and communication development, when the possible effects of birth order, nursery attendance, and multilingual family background were also taken into account. Participants (130 parents of children aged 12-48 months) completed online questionnaires on nursery attendance, language exposure, and experiences with Baby Sign. Language and communication development were assessed using the Bayley Scales of Infant and Toddler Development (Bayley-III) Parent reported Communication subsection. Results found a significant interaction between Baby Sign attendance and birth order, with firstborns scoring significantly higher on the Bayley-III than laterborns in the Baby Sign group. Additionally, in the Baby Sign group, children from multilingual homes scored significantly higher than children from monolingual families. These findings suggest that Baby Sign may interact with birth order and multilingual development.