I can understand how you feel because I had to transition some years ago from 2nd to K. I teach first now, but one thing you need to keep in mind is that they are not 3rd graders. They are way below what you are used to so don’t up the academics so much. They are just getting out of kindergarten and may still be functioning there initially. Study your First grade curriculum and also look at what K has done or is doing in your building to get a feel for what they need to know and how you can adjust. Best wishes to you!