Psychology study finds secret sibling speech is especially common among twins during the early stages of language development

October 9, 2026 - 23:11

A new psychology study sheds light on a phenomenon that has long fascinated parents and researchers alike: the private form of communication that some young children develop with a sibling. The research found that this so-called secret language is especially common among twins, frequently emerging during the second year of life. At that stage, children are still building their vocabulary and sentence structure, so the sounds they share with a constant companion can drift away from what adults recognize as words.

The study suggests this pattern is not a sign of delay. Instead, it appears to be a natural phase in early language development. Twins spend enormous amounts of time together, often more than they spend with adults, which gives them room to invent consistent sounds, gestures, or word-like forms that carry meaning between them. Parents may hear what sounds like gibberish, but the children themselves may be following their own rules.

As ordinary speech improves, the private system usually fades. Once each child gains more exposure to adult language and begins communicating with a wider circle, the need for the shared code drops. The findings add nuance to a familiar idea, showing that twin speech is less a mystery and more a temporary step on the road to conventional language.