When baby sarah is riding in the car with her parents, she occasionally points at passing vehicles and calls out "see cars," even though some of the vehicles are buses and trucks. this is an example of speech.

overextension of words

Explanation:

When children are still around the age of three they may confuse the meaning of words. As a result they may use one word for different things which are not even related maybe because in their still developing mind they see some minor similarities.

For example a car and a bus both have wheels and travel on the road these similarities may cause a child to refer to them both as cars.

If there are these minor similarities that they observe between things, they are likely to use one word to name those things that show similarities.

This occurs because children haven't really grasped the use of langauge, definition of words and all its collect grammar.