Talk

I'm puzzled why you don't just put it where she can't get to it.
Or just don't buy it!

and is not quite canny enough to cover her tracks, so I'm finding wrappers everywhere.

Where are** you when she is doing this? Can you not hear her opening the kitchen door?

Get rid of the treat cupboard! Both as a consequence of her helping herself and to keep everyone in the family healthy.
If you want pudding etc. then buy it on the day.

Just get rid of the treat cupboard (which sounds unnecessary) or hide the treats if you really can’t go without.

Tbh is she’s prone to chub then she doesn’t need a treat cupboard.

Also is she get enough healthy food at mealtimes? If she's constantly hungry

I have this exact same issue with my 7yo.

He is obsessed with sweets and chocolate and if we ever have any in the house he will find it and sneak it and leave wrappers everywhere.

Will post more later as at work but interested in responses.

Put it out of reach. Explain to her why you've done it. Say that when you can trust her to not take more than her share (don't talk about greed or over eating-just about fair shares) you'll think about letting her help herself again

What consequences are there for the disobedience?

Educate her on healthy eating and why treat food is bad for health and teeth, so it’s limited.
Ask her what healthy food she thinks would be a better option when she feels like having a snack.
Give her choices of healthy food she likes and make sure her meals are filling.
Also, make sure she’s drinking lots of water.

If you can't trust her, move it. We had our treat stuff in a low cupboard and 7 year old knew to ask before taking - he was also told if he did start pigging on stuff without asking it would be moved, but he enjoyed the novelty of helping himself and kept check of what we had in there.

Thanks all for your advice.
I am aware I am going to sound a bit MN Unreasonable Supersoaker on this one, but as there are five of us in the family I don't want to get rid of the treats just because it's causing issues with one of us.
I did move them, but she's pretty determined (got a chair, climbed onto work surface and reached the top cupboard). Obviously will move them again, but for the sake of the other DC would not see this as a permanent solution.

Consequences thus far have been a bollocking stiff talking to, both about health, and about trust. I will admit I struggle with DC2 in this area, as the other two DC are far more about adult approval, which makes them much easier to steer.

A locked box that only you have the key for? Unfortunately that means that everyone has to ask you for the key but if the stuff talking to’s aren’t working and she’s so determined that she’s climbing on chairs then what else can you do?

Boxes for each DC. What's in there is theirs to eat for the week. When it's gone it's gone. No exceptions.

No squirrels has a good idea, although if she is sneaky she would probably just eat other children's treats once she had ran out?

got a chair, climbed onto work surface and reached the top cupboard).

Again, where are you when she is doing this? Why can’t you her her going into the kitchen. She clearly needs to be supervised

Locked box or stop buying them.

if she is sneaky she would probably just eat other children's treats once she had ran out?

In that situation, I find siblings are brutal at pointing the finger and expecting justice! Boxes in their own rooms, thieving absolutely forbidden with direst of consequences.

Once the snacks/treats aren't communal family food, but belong to specific people, it's easier for her to see the moral behind it. That would be my theory, anyway, in the same way people don't generally regard getting one over on a big company as stealing, but wouldn't take £10 off a sole trader for example.

Buy it on a daily basis or not at all.
Fill your cupboard with healthier snacks, she could have a sugar addiction and these are difficult to manage, I had one like this.

And OP says she "doesn't give a monkeys about adult approval" ... but she may well fear the wrath of her siblings!

You must be able to hide them somewhere & 'allocate' treats at weekends or whenever you want, most people (I know I am ) are tempted by 'treats' - I've already finished off two special boxes of chocolates that I bought for Christmas, without sharing them.

if it bothers you, buy them less regularly and/or find a much better hiding place,

With three kids, with the best will in the world it's impossible to constantly supervise a 7yo! Sympathies OP, I have one of mine like this. Not a weight problem but certainly a sneaking one! We do limit total no. of treats in the house, for my benefit as much as anybody else's!!! If it helps, I can think of a few kids when I was growing up who were totally sweet mad. All of them won't now let a single sugary calorie pass their lips as adults, and are bringing kids up on a diet of raw carrots and cabbage

This does sound like my dd and yours sounds just as desperate, climbing eating siblings treats.
Please nip this in the bud, it will only get worse, mine is 22 and has a stash of sugary treats in his bedroom now. There was only one of our dc not sugar addicted.
It's not healthy and can lead to other addictions like smoking, drinking and drugs.
if you can't manage get help from your gp, addictions in children are never something to be ignored.

I’d recommend replacing the snacks rather than banning them outright.

A big fruit bowl with “interesting” fruit they can help themselves to (not just one tired golden delicious and a mouldy tangerine!) Kiwis, grapes, plums, nectarines etc.

Healthier things in the snack cupboard or fridge. Carrot/cucumber sticks, mini ryvitas, individual chunks of cheese or mini Babybels, sugar-free versions of drinks.

With three kids, with the best will in the world it's impossible to constantly supervise a 7yo!

I disagree. Age is irrelevant. If you have 3 kids and one of them is 2yo you supervise. There is literally no reason that should change simply based on age. Supervision should be loosened depending on ability and maturity of the individual. Aside from that it is the kitchen that needs kept an eye on. I still do that with one of my teens!