Are they overweight unhealthy kids? Assuming not as I think you would have said.
Dd has done this to me (recently in fact) taken something she KNEW I'd bought JUST for me - very annoying. Weirdly it was a "healthy" thing she just was craving it.
On that note. You SAY they have suitable portions at meals but as a pp said teens need FAR more cals than adults especially if they're sporty/active - dd is 17 rake thin and I serve her twice as much as me and I'm fat!! She also eats far more snack wise than me. BUT she works full time, walks to and from work, has physio to do daily PLUS goes swimming at least once a week, and gym once a week. I'm home all the time (agoraphobia) plus my own disability makes exercise very difficult. Plus she's still growing - 1.5" taller in last 2 months!
They also need more frequent top ups because puberty hormones, being more active can lead to blood sugar/insulin levels fluctuating more than in adults or younger children.
In addition - girls have hormone cravings. Sometimes chocolate but sometimes savoury (We're both like this it's apparently quite common and is due to cravings that are a desire to replace the salts lost in the blood lost at menstruation) - so are the crisps going around "that time" or if the kids have recently exercised/it's been hot? Girls also have a higher calorie requirement at that time. Plus carbs can help with symptoms like pain.
My own mum started doing a sort of extra meal as we hit teens - straight after school, sandwiches & yogurt, soup, small portion of pasta. Or add in a supper? Cheese on toast, low sugar cereal?
And how big a bottle of squash? If a litre then that will go in a day among 4 kids especially with the warmer weather some parts of uk have had lately. I also hate water plain water gives me dreadful heartburn no idea why.
I only shop weekly (combo of health and limited funds) so when the best stuff is gone it's gone and dd knows that. She'll occasionally say can she have extra crisps/pretzels on weeks she knows hormonal cravings will kick in but I don't add loads.
We do go through a lot of bread which is eaten as toast.
Dd throughout her life I've talked to her about having a healthy DIET overall. No food or drink was verboten (seen SO many cases in my own and younger age groups where the parents were REALLY strict then as soon as the kids had their own money they went crazy buying and eating junk and developed ED's, weight issues, type 2 diabetes - the very things their parents were trying to avoid) because in the wider world the junk is there. Teaching them how to handle that is important.
Talk to them maybe? If it is a competitive thing "Jack eats all the crisps if we don't get there first" maybe let them have a box of treats each with name on and when it's gone it's gone? Put combi padlocks on them if necessary.
I'm one of 3 my brother was a bugger for snaffling the good biscuits
I disagree that shadows snacks for her son are "bad bad bad" pizza - carb, bit of veg if only in the sauce, cheese (protein and calcium), hot dogs and burgers - carbs, protein, iron, some vitamins and minerals. Not perfect "wholemeal cous cous and organic slow roasted veg" type food but not toxic either!
Charliecat I had similar when dd was younger she rarely fancies sweet stuff and hates choc.
"Laughing my head off at those claiming not to like water" why? 🤔 is there NOTHING you don't like?
I too am sceptical that as many mothers on mn as CLAIM so ACTUALLY are as strict as they are re "junk food" doesn't bear any relation to my real life experiences at all.
Also a few people on thread are equating "snack" with "junk" no it just means a small food item or items not a full meal. Crudités and dip - snack, breadsticks and houmous - also a snack, boiled egg - snack