I think it would all depend on what you want to do with the videos. If you'd plan to post them publicly online you'd need permission from the parents, in writing.

If you wanted to go down this route, you might want to make it a regular part of lessons otherwise student behavior might change on camera. So many people get self-conscious or ham it up while being recorded.

It's not something I've delved into, myself, though I can see it being useful both to help a student self-evaluate, and for marketing/promotional purposes.