Youtube doesn’t have great parental controls at the moment, however we’ve heard that there will be big improvements later in 2018. For now, you can turn on Restricted Mode which filters explicit and adult content. It also turns off comments.
NOTE: A lot of the content on Youtube isn’t from trusted sources, even if you see a Peppa pig video, you need to check who made that video because it might not be the original creators of Peppa Pig. That means that the video could have been changed from the original.