Having worked in schools as a special education adie, but worked with all students, it sounds like the kids are already having, "winter break itis". Another words, they are crazy! Personally, I would not have kept them in from recess to have the talk. I would have had them doing specific activities to burst off some energy.
Simon says, "Jumping Jacks", Simon says, run around the playground one time" Simon says, "hop on one foot", etc.
There are ways to use up the kid's energy so that when they are in class, they are more ready to behave and concentrate.
I would have a talk with my child and let them know the consequences at home if they did not do what they were supposed to do in school.