You asked

How do I get my teen or tween interested in healthy eating?

Good eating habits are learned behaviours, they’re not instinctive. So what your child has learned in childhood will travel with them into adulthood.It’s important to understand that while your tween won’t show it, you are her biggest role model. So, if you’re in the habit of stocking the presses with sugary drinks, biscuits and crisps then it stands to reason that your child will follow your lead. Be a good example; keep cupboards stocked with healthy snacks and reserve sugary treats for special occasions.
Take your kids shopping with you.
A really great way to teach your child about healthy eating is to take her grocery shopping with you. It’s probably easier to go alone but it’s also important for them to become familiar with food and healthy eating.Get her to pick out fruit and vegetables she would like to try, allow her to make her own decision.Remember, moderation is key. While we want to make the healthiest choices for our children, a special treat once a week won’t do any harm. 
Make mealtimes something they look forward to.
There are lots of ways to make family meals special. Most importantly, sit down and enjoy your food. Take time to savour the flavours. Children should only be allowed to eat meals at the table and never in front of the TV.Get everyone involved in making dinner. Have the kids set the table or get them to make a salad.Try to avoid making one meal for the kids and one meal for adults. Children take their time warming up to new things, so it’s important to give them time to explore new foods. 
Avoid convenience foods
When it comes to convenience and ready prepared foods, some of these foods can be high in salt, sugar and fat. However, there are some that can be as healthy as home cooked food and can be eaten as part of a balanced diet. Experts agree that cooking from scratch can be unrealistic for some people. Most people rely on convenience foods due to a lack of time. It is not impossible to eat healthily while eating convenience foods however we should check labels and avoid foods high in salt and fat. Frozen fruit and vegetables are as healthy as fresh versions. Rice and pasta are all healthy but convenient foods.
Try not to use food as rewards, bribes or punishments. It’s okay to take the kids out for an occasional ice-cream as a reward, but it’s important not to imprint the idea of food as an incentive for good behaviour. It’ll only serve to foster a negative relationship between your child and food.
Have fun in the kitchen
It’s a good idea to encourage your child to help out in the kitchen. Whether stirring cake batter or tossing a salad, it will help your child become interested in healthy eating.
Kids love eating food they create. By involving your child in cooking or snack preparation, they will be more likely to try new foods. 
Breakfast is so important
Breakfast really is the most important meal of the day. A healthy, balanced breakfast is essential to give your child the right start.After ten to twelve hours without food, it’s important to refuel the engines. Skipping breakfast means your child will be too tired to concentrate at school, are more likely to be overweight and more likley to miss out on essential nutrients.
A healthy breakfast should roughly provide a quarter of energy and nutrient needs. 

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