DK

OP here. Just wanted to extend my heartfelt thanks to all of you who provided suggestions and input. I don’t have a huge parent community to talk things over with, so I found all of this discussion extremely helpful.
Thanks to everyone here, we have a good idea of how to move forward. I can accept that it’s probably not the end of the world to overdo the sugar and TV for a few days. And we will be setting firm boundaries in the future regarding the things that matter most to us (i.e. missing school) and certainly any safety issues (keeping secrets from parents), though it may mean making some sacrifices.