Video download sites often disguise malware as video codecs and programs, so using these sites, especially those that host copyrighted material illegally, is potentially dangerous. Legal cartoons on sites such as Archive.org are generally safe.
Video files don't carry malware, but many video download sites encourage or even require users to install software before they can download files, and these downloads are often a conduit for malware.
Furthermore, some of these sites don't even host the material they claim to host. Sites that offer free and legal downloads, which are often cartoons in the public domain, are generally safe, especially well-known sites such as Archive.org.