These are obviously well done simple 3D animations. The "graininess", as you say (see NOTE1), is intentional, it's not caused by missing knowledge. It can be aimed to create a mood or it can be done to save space or computing time. It can be got by reducing model complexity, rendering accuracy or pixel resolution or all of them mixed. If kids made these from the start, they must be quite skilled kids. It needs something more than good will to generate 3D models, to make them to move or at least the camera to move and to insert, maybe even to create some music which fits.
Some ability to work with 3D models and animated videos is still needed if the 3D models are downloaded from an external source (there are numerous free and commercial).
It is, of course, possible that some of these are compiled and post-processed from captured video game scenes. Even it needs some skills.
How to make one:
Get a 3D program, a screen video recorder and a multitrack video editing program which accepts your screen recordings as source clips. The 3D program can be for ex. SketchUP. Download from its Warehouse a free 3D model of some object or more complex scene.
Make numerous screen recordings where you pan, rotate and zoom the 3D scene or make the camera to fly around.
Draw some simple images which have transparent background so that the images can float in the video.
Get an "easy music builder" which contains thousands of ready to use rhythmic and melodic phrases + noises + simple enough combining frame to create easily some modern music. Magix Music Maker is a good example.
In video editor try to combine your screen recordings and drawings so that you can insert some music, too. You can insert some pan and zooming effects also in the video editor for more complexity. The whole video effect repertoire can be used for the same.
If you want to make some advanded looking with static non-moving objects you can try simultaneous camera moving and zooming for apparent object movements. In reality only the perspective changes but some object seems to become closer or go further when some other seems to stay in its place.
If you are not musical, insert weird noises like the maker of the wireframe street flight video has done. I guess some planning pays off. I guess it's avoided in the wireframe street flight video.
Finally render the video. Use low pixel resolution to get the wanted "graininess".
NOTE1: Term "grain" is reserved for certain type of noise in photos and software effects which simulate it. An extreme example: https://www.publicdomainpictures.net/en/view-image.php?image=276395&picture=grainy-image-of-a-shadow That kind of grain does not exist in your video examples.