I just stumbled across this really neat free resource recently. Kids Discover Online  has tons of interactive lessons, videos and so much more available for students. They do have a monthly cost for unlimited use, BUT you can register for a free account and have access to up to 200 free lessons. That should get you through quite a few weeks if used as a supplement.
They have several options to choose from in science & history – astronomy, historical figures, time periods, etc. Go here  to create your free account or click the graphic above.
Also, check out all the FREE online Homeschool resources on How To Homeschool For Free!