No, they are based on toddlers. The teletubbie world is an abstraction of what the creators remembered life to be like when they were children. The narrator represents an adult carer figure, such as a parent, guardian, or nursury supervisor and the show deals with the interaction between toddler and adult agendas and perceptions.
Here is what co-creator Anne Wood has to say about them:
Children, especially little children, live in the same world as the rest of us but perceive it differently. So the most important thing any adult can do for a child is to listen to them and try to understand them. Children love to be listened to - so when Andrew Davenport and I created Teletubbies together, we spent a lot of time observing and listening to children. We tried to find our own way back to feeling how we had felt as children and also shared what we had learned about their different perceptions. Along the way, we realized that the difference between an adult agenda and a child's agenda can often be very funny, so we had a lot of fun - and placed the notion of fun at the heart of the program.
You can read more on the PBS website...
With this in mind, we can see that the restricted world in which they live represents the restricted world of the child, with the the narrator, the wake up call and the windmill signifying bedtime representing the influence of the adult agenda.
This closeness to a representation of how a toddler sees the world apparently explains why they relate to the show so easily.