This has happened on numerous occasions, things I have in the cupboard, and also some of siblings saved sweeties. I do hide things, but dc finds them. Recently an entire bar of chocolate went missing, and we asked dc directly if she had taken it, and she denied it. The wrapper was later found under her bed. She does get pocket money (under £1) weekly and is allowed to spend that on sweets, and there is also very often dessert after meals, so she isn't being denied sweet things. We have spoken to her about it, and said that we don't like it, and want it to stop, it is bad for teeth/health to have to much etc. and that the most upsetting thing is her lying to us because we then feel that we can't trust her. She did listen on this occasion and seemed to take it on board, but next time was alone in the house took things again.
We are not sure how to deal with it. Perhaps it isn't a big deal. I don't want it to lead to casual taking of other things. I don't want her to eat loads more sweets, or for her to feel she needs to take things in secret. I don't want to feel like I need to lock things away, or that she can't be trusted. I also don't want to look for a square of chocolate of an evening and find it gone! How would you approach it?