keep an extra eye on Charlie being that he is young.
Any sign of infection, such as asnotty nose or gooey eys then call the vet.
We took Jasper to the vet at the point where he would not eat, not even soft food and the weight was falling off - he also had green snotty nose and was clearly under the weather. As he got antibiotics we took Poppy to the vet too and she ended up with antibiotics although nowhere near as bad as Jasper (despite him being the one that had had the KC vaccine

)
You know your dogs and unless they seem unwell I wouldn't rush to the vets - not just becaise of the financial cost but like Polly says, antibiotics for something that will clear on its own seems silly for the dogs.