The Teletubbies' language is evidence. Their simple and repetitive words mimic how toddlers start to communicate. Also, their playtime activities, such as dancing and rolling around, are things that real small children do. Moreover, the way they show affection for each other, like hugging, is based on real - life children's behavior.
One piece of evidence is the way the Teletubbies interact with their environment. Just like real children, they are excited by simple things like a flower or a ball. This reflects how young kids in real life are easily amused by the simplest of objects.