Although I allow him to watch Youtube, it is important to make sure that he only watches it for a limited amount of time to avoid any 'addiction' issues.
Here are my favourites.
1. Super Simple Songs
This channel has plenty of classical nursery rhymes and their visuals and graphics are really well done! I thoroughly enjoy watching their videos together with my son. Besides that, some of the nursery rhymes has been simplified so that your little one whom has very limited vocabulary can also sing along =) If you are bored with the usual nursery rhymes, they also have their own original simple nursery rhymes which are easy to sing along such as Walking In The Jungle, Little Snowflake, Wag Your Tail, My Teddy Bear and so much more.