Following is a list of fun learning websites I currently have bookmarked for independent use in our homeschool. (Meaning these are websites the Agents—third grade and first grade—primarily access and play around on themselves, not ones I scope out for lessons plans and printables. That list is coming soon, though.)
Some are mostly game-oriented while others are a combination of games, fun facts, videos, pictures, or other stuff. The museum/zoo links are all places we've visited in person.
All of these would be appropriate for kids around ages 5-9-ish, although some might be a bit much for the younger end of that range and others would be suitable for older ones as well.
Where appropriate I linked to the "kids" page, or wherever the Agents tend to start exploring, instead of the main page. Every site listed here is free.
Natural History Museum (London)
Owlie Skywarn (weather)
Science Museum (London)
Sphinx Kids (music)
World of Brian P. Cleary (mostly language arts)
Hope you enjoy checking out the list and find it useful and fun.