The word "what" can be singular or plural depending on context. A child could be influenced by what (programs) he or she watches on TV... A child could be influenced by what (program) he or she watches on TV... Both are correct and you can see the first is plural, the second is singular. So without the word "program/programs", you have to use some previous context. Since there is none, you are free to think of it as singular or plural. So you can say either of the following: most of which are most of which is The word "those" can only be used with the plural version. In my opinion, it is awkward to include that word. I would say: A child could be influenced by what he or she watches on TV, most of which is not meant to be viewed by the child's age group. That sounds the mast natural.