Don't restrict their diet just because of a hole in their tooth. As you said, their diet is pretty good and TBH, I think all that stuff about sugar giving you cavities is bull****. If you are worried about it, make sure that they have a drink of water after eating something with sugar in it to remove any traces of it, but don't go all hard-assed and make your kids miss out FWIW, my 4 kids all have exactly the same diets, they all brush their teeth twice a day, they only get flouride from the toothpaste (tank water) and two have the crappiest teeth you've ever seen and the other two don't. Once my DD1 had multiple fillings in a single visit because she just has terrible teeth. Not once was I ever told to cut out all sugar, but I have been told plenty of times that some people just have bad teeth. And I used to work as a dental nurse so I saw a lot of kids with cavities in that time.

But do what you gotta do. If cutting it out makes you feel like you are being proactive about it, then its not a bad thing i"m just saying that it may not make a difference.