YouTube Restricted Mode
Do you talk to your children about the different videos/channels they watch and to check if they have their own channel and upload their own videos. Have you ever looked through their watch/search history? Many children say their parents don't know they have their own channel!
YouTube has a restricted mode which can be enabled to allow parents/carers more options over the content their child has access to.
Help video for setting this up can be found at https://www.youtube.com/watch?v=UFC2rbIJdnI
Or for increased restrictions, you may consider YouTube Kids https://www.youtube.com/watch?v=gtjXhK4_Mxo