From nhs:
Fruit juice and smoothies
Fruit juices, such as orange juice, are a good source of vitamin C. However, theyalso contain natural sugars and acids, which can cause tooth decay.
Babies under six months oldshouldn'tbe givenfruit juices. Diluted fruit juice (one part juice to 10 parts water) can be given to children with their meals after six months. Giving fruit juice with mealtimes(rather than between) helps reduce the risk of tooth decay.
From agefive,it's OK to give your child undiluted fruit juice or smoothies, but stick to no more than one glass (about 150ml) a day served with a meal.
(Squashes, flavoured milk, 'fruit' or 'juice' drinks andfizzy drinks*
These are not suitable for young babies. These drinks contain sugar and can cause tooth decay, even when diluted.
For older babies and toddlers, these drinks can lead to poor appetite,poor weight gain and, in toddlers, diarrhoea. Even drinks that have artificial sweeteners can encourage children to develop a sweet tooth.
Watch out for drinks that say 'fruit' or 'juice'drink on the pack. These probably won't count towards your child's5A DAYand can be high in sugar.
Fizzy drinks are acidic and can damage tooth enamel so they shouldn't be given to babies and toddlers.
Diet or reduced-sugar drinks aren't recommended for babies and toddlers