Is their mom not feeding them? That is concerning
Or say sorry these snacks have to last us all week we’re on a budget so I can afford my baby’s formula
I hope the mom isn’t using you to feed her children. If they say you have the good snacks then that either means they have no food at home or either the mom has food they don’t like to eat. Hard to say what to do not knowing the dynamic. I would definitely set boundaries and lock your door if you have to to keep children out of adult bedrooms. The mom should not be letting her kids behave like that. I was brought up similar I guess because that would’ve been considered rude behavior if me or a friend acted like that as kids. Unfortunately, people don’t parent their kids these days and are too lazy to do or say anything. Hope you find a solution. 
She wouldn’t be my friend 
if we ever go to another person’s house I take food snacks with me, I don’t expect my friend to feed my kids. This so called friend is rude as hell for not pulling her kids into line.
You let it, and the faux friend and her rude brood go. Permanently.
This is no friend.
The formula afford v pizza comment says it all…and she will do nothing but get defensive and offended if you try to set boundaries with her about anything…and its not your job…to teach & corral her kids for respect in your own home.
She’s entitled and she’s the one who has taught her children its okay to behave the way they do without any discipline or manners to be respectful in others homes. Wth…were her kids even doing in your bedroom?? Its not okay…and the mom …knows exactly what she and her kids are doing.
None of this is worth it for this advantage taking, rude, entitled judgemental person with kids in tow running amok in your home you’ve been calling a friend.
She’s not.
Ditch her, and find other playmates for your children.
Atp…you are allowing all this.
Does the mom not feed them at home? Because it seems like they’re eating everything they can WHILE they can.
It could also just be that they really like the snacks you buy.
But 100% agree. There needs to be boundaries. Next time they’re over, sit the mom down and explain to her that it isn’t acceptable for you to ALWAYS have to be buying more and more because they have no self control in the situation. Tell her that while you love her and you love her kids, they cannot constantly be scavenging for food or tearing through your things. Let her know that there is going to be a few snacks out and that she should instruct them clearly that they are not to access the pantry or refrigerator. If she gets mad, she’s not your friend.
“They’ll have an entire box finished off by the time we leave” 
The audacity!! I’d be like you need to leave now then if you can’t replace the crazy amount of stuff your kids are eating. That’s extremely rude. I understand a couple snacks here and there but it sounds like you’re being taken advantage of and that is NOT a friend.
Children have absolutely no business in a parent’s bedroom whether they’re your kids or someone else’s. If you must, lock it!
I can’t believe she had the nerve to say how can you afford formula for your baby and not pizza for HER kids. I like the snack box idea. If they don’t like it ask their mom to bring snacks when she comes. Or text her and tell her to grab a pizza on the way over. People will only treat you how you allow them too
It sounds like the kids don’t get fed well, maybe the mum brings them over so they can have food.
Really got to say something or make sure you don’t have any of the “good snacks” available then say you could afford to keep replacing them.
As they said you need to buy formula for the baby, you can just say you have more important things to spend money on then buying snacks and take away.
No talk to the mom tell her that they are welcome but they won’t be getting any snacks and they can’t go where you can’t see them… that’s extremely disrespectful and your friend should know how you feel you’re not the asshole for not wanting kids that’s not yours to eat you out of your own house and the fact the kid is getting an attitude about you not ordering food id say you can ask your mom if you want food simple. Food isn’t cheap! Don’t let them run your house. They are guests. If they don’t like it then they don’t have to come over
Girl take control of your damn house. This is your house and your rules. We don’t get snacks every 15 minute you get one snack while here ! If they’re that hungry their mother can feed them before they come or after they leave! Absolutely not. As far as them asking you to spend your money next time wake their mother up and say your children are hungry you need to tend to them! As far as them asking if you don’t have money for so n so bud u can do this. U tell them that’s for adults business and children to mind their own. Apparently their mother isn’t setting any type of home training so you need to set boundaries! When they’re in your cabinets tell them to get out this isn’t their house if they would like something. Ask for it not take !!! It’s clear your friend has no respect for you or your home so unfortunately you need to speak tf up or end the friendship