Getting more views to old channel


I have a youtube channel in the kids niche with about 4 Million Views and 8000 subscribers. The majority of the views came in the beginning of this year up to early summer, until I (unfortunately as I know now) changed the description and tags of one of my most successful videos which brought me about 35.000 views per day and from that on my views on my channel dropped, fewer people subscribing etc. Because I was busy with other things in the last couple months I stopped uploading more videos to my channel, and as you can guess when I started uploading again a few weeks ago, my videos got even less views, barely any, even if I have about 8000 subscribers, my last videos got less than 50 views each. I still see channels with the same type of videos getting a lot of views but I don't know what I can try to do to get suggested/recommended next to them again. It's frustrating to put in the amount of work and money to make these videos and then getting nearly no views, even if I have exactly the same quality, length, title, description tags, as my competitors. I just need a way to 'revive' my channel, if my videos get recommended again I am pretty sure they will be successful because they're of good quality and like the other successful videos, but I don't know how to 'kickstart' my channel again? Does buying views or something else help? backlinks? Using not only the same keywords as my competitors, but lower competition ones? Do you have any advice for me? Thank you