By Default, students are not able to access Youtube Directly. The only verified way for students to watch youtube videos is for the teacher to create an assignment in Google Classroom and embed the videos as part of that assignment.
You cannot simply drop a link to the youtube video, as a link will just try and route them to youtube and that is blocked for students.
Use the link below to watch a short video that will walk you through the process of embedding a youtube video as an assignment in Google Classroom.
If you follow the steps in the video, and your students still cannot watch the video, please open a support ticket and be sure to provide us the direct link to each youtube video that is not working for the students. We will also ask you to verify with us that you have watched and followed the steps in the video linked below.
The link below shows how to properly embed a youtube video as an assignment so students can watch it.