There’s a bunch, and it depends a lot on what you specifically want to get out of it.
If you’re looking for something like a ‘regular’ class, then https://www.khanacademy.org/ is pretty dependable especially with regards to math. It’s basically just math classes online, with walked-through examples and such.
On the other hand, if you’re thinking of finding educational material that your child might enjoy watching in-between work, https://www.youtube.com/user/crashcourse has bright, colourful videos covering a lot of topics from history to science. This is a lot less in-depth than a class, but it’s also probably easier for children to digest while staying engaged.
Either way – hope this helps!