Here is a video on how I brush my own children’s teeth… in about 30 seconds and get every single area like a dentist dad does. You can only “get away” with less brushing if you are very picky about the foods you give them during the day. For example, if you give your child an apple and cheese, there is nothing to brush off afterwards. If you give your child an everyday cracker, you may need to brush for two minutes after every snack time.
As far as actual brushing technique, if you know exactly where to go, you can reach all of the areas that are usually missed (I know where I fix cavities at work all day, so I know where to focus on.) When your child turns 6 or 7, then convert to two minutes twice a day. If you are giving your child the right foods, you can spend less time brushing their teeth under age 6. Doesn’t that sound nice!