So what do you do to them, when they do this????
There has to be some kind of repercussion....
They are controlling the household. If they do this for food... what else are they doing? And not listening to you???
They also know, you are "busy" with baby.. .and are not easily nor quickly able to get to them... they are 'faster' than you... and you said they "plot" how to do it.
How OLD are they????
You really need to stop buying these foods/snacks... or you have to put them somewhere else.
OR, research different kind of locks... for the cabinets. It seems to be a NECESSITY, in your case. Or they will keep doing it.
Also, they don't eat 'meals.' And only snack. Just take away the snacks... and if they starve they starve.
It is a game to them.
They out think you....
If they scream, they scream. DO NOT GIVE IN to their screaming. Don't give them any food... since they waste it anyway and refuse to eat it.
TELL them this.
The book "Have A New Kid By Friday" is good for ideas... and not derogatory. You can get it from Amazon or even E-bay.
Do they have any type of discipline or punishment???
Have them WORK for their "food" or treats. They are old enough, I assume, to be doing simple chores. ENFORCE this.... list it down on a paper you post up in the kitchen. Have them wipe tables, pick up toys, do things for each other and you.... tell them, they have to do an "x" amount of things, for the FAMILY... meaning, each other or you/Husband, to EARN treats.... EACH day. And you check it off on what they do or not. Daily. THEN that way, you also have a tangible and visual thing, to SHOW Daddy... when he comes home.
Do they do this when Daddy is home too? What does HE say about it????
Sit them all down, in a family meeting... and clearly, state the "problem", their consequences... and what they can or cannot do.
And if they do not cooperate.... then, you do whatever repercussion, you have all "discussed." Mind you, you don't let THEM decide the repercussion... YOU and Hubby, state it.
Or you take away their toys etc. That's it. And put it where they cannot get it. They have to earn it back.
I would, start making them responsible... for their disrespect...
Also, you can make a SEPARATE box... for "their" food/snacks... and ONLY from that box, they can grab things from. Maybe they want what you buy for Lunch Bunch, and they want the same things, too, at home. TELL them that things cost money... too. At this age, you can tell them ideas like this... make it a lesson... my son is only recently turned 4... and he KNOWS that some things cost more than others..... and that "wasting" something wastes money. We teach him that. If he wastes something, carelessly, then I don't buy it next time. For example.
all the best,
Susan