Honestly if you just brush their teeth before bed it isn't a problem to give them juice during the day. I grew up in a dental family and was always told to brush my kids teeth as soon as they start erupting. You can even get them used to it by brushing their gums when they are infants so they don't fight you. Juice and cola aren't going to eat your teeth immediately it is when it is allowed to sit on the teeth. My kids go to bed with a waterborne of water and have since they were toddlers.