If I want to treat myself to a nice bar of chocolate or a treat i'll do it away from the kids such as at work, or if i'm shopping alone, visiting friends etc.
Why though? You are hiding the fact that you have something different that they don't have, which I don't understand at all. I am upfront about it & honest, they know that X in the fridge, or Y in the cupboard is mums, just like the cake we bake is for them (I don't like cake)
Example. For my birthday my friend made me a cheesecake. As far as the dc were concerned, it was for everyone, because I didn't say differently & because it was.
I didn't have a piece straight away as she bought it over the night dh took me out for dinner (she babysat). I went out the next day (all day). Following day I didn't have any until after dinner & it was mostly gone. The tiniest sliver left!
It wasn't huge, but unbeknown to me, dh allowed them to have some while I was at work & let older dc cut it. Dh also had some. After school they asked for some (dh still at work), so not realising they had already had some, I said yes. Again, oldest dc cut it. When I wanted some, there was barely 2 mouthfuls left. Yes, it was annoying for me, but as I said, the food was for everyone.
My point is that left to their own devises, dh & the dc will eat the food we have in the house as soon as they see it. I can take it or leave it & just have one or two pieces of chocolate for example. They seem to need to devour it in case it disintegrates.
If I had said that the cheesecake was for me, they would have respected that & left it, & knowing me, we ALL would have had a piece after dinner.
So why shouldn't have a little something that they know is mine & off limits, so you know, I can actually ENJOY something that I bring into the house?
After all, when they go to work, they can't just help themselves to the food in the fridge and/or cupboard that might be their colleagues lunch!
It about respect & boundaries, in my opinion.