In the case of an eleven year old downloading songs off the computer to play in an amateur video, it is possible that their use of the music could be considered fair use. However, this would depend on the specific circumstances, such as the amount of music used, the nature of the video, and whether the use of the music would harm the market for the original work.
If you are not sure whether your use of copyrighted material is fair use, it is best to err on the side of caution and obtain permission from the copyright holder before using the material.
Here are some additional resources that may be helpful:
* [Copyright for Kids](https://www.copyrightkids.org/)
* [The Fair Use Doctrine](https://www.copyright.gov/fair-use/)
* [Copyright and Social Media](https://www.copyright.gov/social-media-and-the-law/)