Children need to brush "2 X 2". It means brush two times for two minutes. A lot of people think toothpaste as soap. The toothpaste company, Proctor and Gamble, love you to think that way. But that is not true. The toothpaste is more like medicine than soap. Because it is medicine, it has to linger in your mouth long enough to do the work. That is why two minutes is important. Average Americans, both adult and children brush 55 seconds, not even a full minute. You can get huge benefit by not rinsing with water after brushing. But most people don't like the taste of toothpaste to linger and most people don't need to go that far. Still in some case of people who don't brush while in braces can prevent the cavity.
For adults, it is get even harder, "3 x 3 x 3". The first three means that you have to brush three times a day. Yes three times a day. No compromise. If you stive for three times a day brushing, you will fall off to two once in a blue moon. That is much bettter than trying to brush two times a day. Again, key to success is not to make compromise.
The second three means that brushing for "three" minutes. When average American brush less than a minute, brushing three minutes can be seem ethernity. Once you try it, you will see how long the time is. The goal is for toothpaste to linger long enough to effect. So three minutes without compromise is the goal.
The last "three" is something that even my wife didn't get it. In fact, I have never met anyone who even guessed it right. Answer is that you have to brush within three minutes of your last meal. In other words, you have to brush right away rather than half an hour later. When you eat a meal, technically your mouth become acidic like car battery or soda. When you brush right away, the toothpaste neutralize and get rid of plaque right away before the plaque get stuck to the teeth and become hard stuff called tartar.
In summary, for kids, brush twice a day with two minutes.
for aduls, brush three times, for three minutes within three minutes of eating. Is that simple. Period.