It is always better to give your child a piece of real fruit over fruit juice for more nutrition. In whole fruit the fibre slows down sugar absorption reducing spikes in blood sugar levels. The extra fibre is also good for regular bowel health. Juice from 100% real fruit can provide nutritional support to picky eaters who have a hard time eating the recommended fruit and vegetables in a day. In most cases, juice should not replace a healthy whole foods diet.
There are a few issues with giving your toddler juice. One is that it trains your toddler’s taste buds to expect sweet flavours all of the time. Secondly, when given to a toddler to carry around all day, it can increase the risk of tooth decay. If juice (or milk) is given at night time in a bottle, this can leading to severe tooth decay called “bottle mouth” or “bottle caries”. A serving of juice is considered to be 125ml (1/2 cup or 4 ounces) but some toddlers are given a lot more in a day and excessive amounts have been linked to obesity, chronic diarrhea, and a reduce growth rate (short stature) in children*. Two strategies to introducing juice include watering juice down to reduce the sugar content and making sure your toddler is brushing their teeth at least twice per day.
*Nicklas, T., et al. 2008. Association Between 100% Juice Consumption and Nutrient Intake and Weight of Children Aged 2 to 11 Years. JAMA Pediatrics 162(6):557-565.