changing an active voice sentence into passive voice

the baby was sleeping in the cradle

hi ! As I know, in English there is some sentences, some situations that we can not change them from active form to passive form, and now I think it's true in your case.
I give you 1 more example to make it clearer: "I am from China". you can not change it become "China is come from by me". It does not make sense.

Akitadunk, you are right. Some sentences cannot be changed from active voice into passive voice.

:hi:

Your sentence does not have a direct object, as in:
"I hit the boy" where 'the boy' is the direct object.

Then, in passive voice it would be:
"The boy was hit by me."