DS had 2 weeks off, which was filled with visits to our parents' houses, gifts, fun trips, etc. Now that he has to go back, he has been giving us a hard time

He won't go play with his friend or his favorite teacher. We used to just be able to say bye and give him a kiss and he would be fine. Now we have to signal the teacher that we're leaving so that she can find something to distract him with otherwise he runs out of the room.
Re: Anyone else's LO have a hard time going back to school after winter break?
Sorry you're having trouble. We actually are in the opposite situation. We were at our wits end before Christmas, but 2 weeks off being best friends again (rather that constantly frustrated about her behavior at home and school) seem to have hit the reset button. She seems to have made a conscious choice that she's not going to do the things she was doing before (basically just refusing to do what she's supposed to do, especially in circle time).
I'd try to stay super positive with him, and don't talk about school at all. If he's feeling anxiety, being put on the spot about it will make it worse. My goal for the winter break was to show her how much I love her, and like her, and put absolutely no pressure on her whatsoever.