The top cavity-forming snack is actually Goldfish cheese crackers, IIRC. Because the snack sticks to your teeth really well and carbs get broken down into sugar anyways. Plus kids are worse about picking their teeth clean with their tongue; Adults will absentmindedly pick at their teeth much longer, but kids tend to lose interest quickly and just leave stuff stuck to their teeth. And since goldfish is a common snack for kids, all of that combines into Goldfish being really horrible for causing cavities, particularly in kids.
This is a legit tip. Using electric brushes or waterpiks is a good practice, but it does not address the main issue. There's too much acidic content in modern food, and we as a species are not able to keep up with this high abundance of highly processed foods. Also, I'd add other acidic beverages, like coffee and citrus juices too.
Sugar is a primary source of food for the bacteria that make up plaque. If you feed the bacteria, they will grow. As you can't eliminate 100% of the sugar from your diet, teeth care is always going to be required. Less sugar, however, means, slower growth.
Also. Just like dogs have dental chews that help to clean their teeth, eating other non sugar foods can assist with controlling plaque. Vegetables in particular are helpful, but even something like chewing on beef jerky acts as a sort of scrub brush for the outside of the teeth.