Kamlesh S.

It depends on your goal. If you are looking for your child's brain development and also his musical skills, then you can go with some courses which are designed for the same, eg. Trinity School of London or any other 
but if you are interested in playing Hindi Ragas or bandish on the guitar, then definitely Indian classical music.

It depends what you want to sing but if you wish to sing melodies than yes you need to know the bit of classical for riyaz and especially ornaments of singing like Khatka Murki and Gamak you should practice it.
If you wish to sing rap, jazz pop, punk, soft rock than you don't need these training only you need to know the scales Rhythms and a bit of vocal exercise

See growing you career on youtube is not easy and it is also not impossible. to be practical now a days you have lots of competion but still there are so many waysi will try to list here few

1. Learn singing from a well knowledgeble person that is the first and the basic requirments

2. try to set up a small home studio if not than record your audio video 

3. once your project is ready than find a promoter or distributer on youtube and seek a help from him to promote your good work

4. and than proadcast on his channel you will find so many promoters giving new singers a chance

always remmeber if you have diomond voice but if there will be no promotion than its not of uses