Soundcloud is just fine
This review is pretty ludicrous because it's pretty safe if you avoid certain things. If you want to shield your child from this site since there is some inappropriate things here and there, you might as well ban the internet from your kid. There's gonna be inappropriate things EVERYWHERE on the internet. If you just have your child steer away from inappropriate songs and content on the site, it should be fine.
Anyways, the site is relatively easy to use. It has a pretty straightforward design, you can easily search for songs, and easily do many other tasks. You will need to make an account to like songs, make playlists, and upload content. Soundcloud does go down frequently, so please do understand that.
Overall, it's a pretty cool site, and I think it's fine for a child at least 10 years of age to use.