I would rather have a child mind in an adult body because during childhood people are normally creative, curious and want to explore more. However, because they are still children they cannot explore as much.
If a child had an adult body they would have a lot of freedom and more resources to be able to be creative and innovative. They also have no parents to stop them from pursuing their passions and limit their curiosity. Life will also be more enjoyable as it will less boring and full of joy, curiosity and creativity.
If you had an adult mind in a child body life would probably be more boring than have an adult mind in an adult body because you would have less resources available than an adult and you won't have the same joy and exploration that you normally would have as a child .