You should never give juice to a baby under six months of age. There is no nutritional reason to do so, except if your baby is constipated and then small amounts of prune or pear juice can be given, as directed by you child's pediatrician.
If you offer juices before the introduction of solid foods, you risk the child not taking enough breast milk or formula. As for toddlers, there is no need to offer juice if the child is eating fruit. Why? It is packed with sugar, and children that get used to drinking juice often won't accept water. This can lead to over consumption of sugar, tooth decay, and obesity as they grow.
Children of this age need 2 to 3 servings of fruit per day and only one of these servings should come from juice. If you decide to do this, remember that 4 oz. is a complete serving for a small child — you should never offer more than 4 oz. in one day, and it is best to dilute the juice with water. You should at least make it a 50/50 mix (though you may want to make it more like flavored water). If the child hasn't had juice in the past, they won't even notice the difference. If you've already been giving juice and want to cut back, wean your child off slowly, increasing the amount of water each time.
Also, if you do decide to give your child juice, make sure the label indicates that it is 100% pasteurized juice, and always offer it in a cup — never in a bottle.
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