Aww big hugs
Honestly rodents (mice especially) can get through the TINIEST gap. And they can get all over, jumping and all sorts. I'm not saying that to scare you, just that it's not really unusual if they get to a place you didn't think possible, because they're crafty little buggers.
It's kind of gross to have rodents, but don't be embarrassed. It's happened to me plenty! It happens to loads of people, they're probably getting in from outside, it's probably not an actual infestation or anything. I think this is the only house I haven't seen at least a mouse in. Older houses especially tend to get mice easily. My last house didn't have a rat problem (I mean I'm not totally clean/tidy but I like to think I don't attract an infestation of rats) but the area had a LOT of rats, so if we ever left food out, the rats would get in. We had to be so careful! You could literally see the rats running about on the street outside, we lived next door to a recycling plant and in front of a farm, honestly I've never known anywhere else where rats are simply running about all over like that it was awful. But if you're really stringent, you can definitely keep them at bay.
I would put everything in containers. Even stuff high up, because they would still be attracted by the smell. If you haven't seen any rodents/seen droppings etc, chances are you can get rid of the problem quite easily if you're totally strict about not leaving plates on the side, getting containers for all your dry food, that sort of thing. Even stuff like empty beer bottles, get rid of them, the smell will be attractive.
Like PP has said, block even the tiniest holes with wire wool.
What we learnt the hard way is that if you put rat poison down, they will often go to some dark hole in your house to die. I cannot stress that enough. We learnt that the hard way
. Whatever you do, use traps. Having a decomposing rat in a hidden location in the house was far, far, far, far worse than having a live one. We literally couldn't use half the house because of the smell! It was so awful, I can't describe. Finally after about 2 months of puking every time I used the washing machine we found it wedged between the pipes half way up the back of the fridge.
But with a few traps and removing all the temptation I think you'll be absolutely fine! Doesn't sound like you're exactly overrun. If you get rid of all the food, chances are they won't be tempted back inside anyway and you won't even see another one.
Try not to stress too much. It's really common, in the case of mice especially it's just a hazard of living in a house that isn't brand-spanking new, and it's generally easy to eradicate. I would definitely recommend traps not poison though. I bet you can get rid of the problem without ever actually seeing one unless it's in a trap. xx