So a better option would be to tell them just what to expect:
"Ladies and gentlemen and cabin crew, please pay attention, this is your captain. We had a problem with our left engine and we have chosen to shut it down. For safety reasons we will return to XYZ for a completely normal landing. If you smell or see a little smoke in the cabin, this is normal and comes from the engine through the aircondition and is harmless. We will be busy the next 15 mins to complete our checklists and set up for the landing, for that reason further information when we are on the ground. At this time I ask everyone to remain seated with you seat belts fastened and await the landing. Thank you."
Speak unusually slow and make a pause between each sentence. Since your adrenalin probably is a bit up it will ensure that you actually speak at a normal pace.
Followed by an intercom ping and asking the Purser if she copied that and if she has any questions and telling her and the girls to remain seated as well.
Very poor- never ever make a PA to the cabin like that until you have briefed the cabin crew first, unless you have little time before landing. The cabin crew are part of the operating team (remember Kegworth). You brief the team first and give them time to brief each other-then make your cabin PA.