The design used for kids should always be simple as well as colorful and cheerful. Images or cartoon characters (if being used) in the design need to look cute and always use bright colors. No need to have much words in the design. But more like telling a story through the images.
Teenagers:
Well, teenagers like to have trendy and quite funky design. It can be quite messy depending on the topic. They tend to like violent-looking font style and crooked text style. It's okay to have more images in the design because teenagers always like it.
Adults:
In contrary, adults like neither simple nor trendy. Well, simple is good but works better if it's not too simple like designs used for kids. Some adults like simple design with a minor mix of classy and classic touch in it. For adults, appropriate usage of words is important as they care more on the contents.
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