It is a common mistake to think that streaming video is necessary for an online tutorial. At best it can be interesting but at worst is can undermine the entire tutorial.
Video conferencing works well enough between adults in the context of a meeting in the office, but an online tutorial does not need a video link.
Instead of watching the shared whiteboard, a child will focus on your face rather than what you are saying. With a voice however, the child is more inclined to watch what you are writing or drawing on the shared whiteboard which is critical for their understanding.
If you are explaining how to work out long division, the child should be watching what the tutor is doing, not watching the tutors face. All that matters is the voice.