Dear Miss Deborah Broughton:

You wrote:
> Can you tell me if ‘Once upon a time there was a little bird called
> Tweetie’ is a simple/complex sentence please??
>
This is a simple sentence. The subject is “bird” and the verb is “was.” There are no other subjects or verbs. “Once upon a time” is an adverb followed by a prepositional phrase. “Called Tweetie” is a participial phrase modifying “bird.”