Tell your child that you are going to say a sentence and that they have to help you stretch it by adding a word to it to make it longer.
Then you add another word and continue to take turns adding words until you have a long sentence (that still makes sense).
For example: You say ” The kitten played.” Then it can become ” The white kitten played”, “The white kitten played outside.”, “The white kitten played outside with a ball.”, “The white kitten and the dog played outside with a ball.”, etc.
This game can be adapted for many different ages. You can leave it like it is for younger kids (and keep the sentences shorter) or you can add some requirements to make it harder for older kids. Add things like: “Now you have to add a noun, adjective, pronoun, adverb, etc.” or you can have them write out the sentence when finished. this is a great game for developing vocabulary and practicing extending sentences so that they are more detailed!