Hi there, I'm also a mother of two children and I know what's the importance of a balanced diet for child aged 12 years because it is the growing age and children need most vitamins and minerals during this span of age. My children never gave me such nightmares by not eating proper diets and not drinking milk or juices but if your child does so then I have various options for your child. First of all, you can try out Fruit smoothies, these drinks are children's favorite and they binge on them like anything. If your child likes them too then you can try out different flavored fruit smoothies for him and these drinks are a healthy option for kids as well. Next option that you can try is Fruit Squash, this is another healthy drink that children love to drink, but they are full of sugars so you should try and use those fruits which contains less natural sugars and if you are preparing it on your own then you can manipulate the amount of sugar used, so that it turns to be a healthy option for your kid. Last option that I would advise is the juice of his favorite fruit mixed (disguised) with juice of some other fruit. These were the options that I knew regarding healthy drinks for kids, I hope they work out for your kid.
