8 year old son suspended from school

So my son has been suspended from school because his teacher caught him googling “How to kill somebody and get away with it”. I asked him what his reasoning was in being interested in this topic he said because he was watching something on YouTube that showed people robbing people and killing them but never got caught. Come to find out he watches a puppet on YouTube named Jeffy. I watched a episode of this jeffy character and he is terrible. He talks about committing suicide and other disturbing things. I’ve told him a number of times I didn’t want him watching anything vulgar and I’ve explained to him what vulgar means. How do you block these type of things on YouTube? I have a TCL Roku tv.