I've thought for while now the same thing as Tom March, that there is a short supply of actual learning activities on the web. Yes there are quite a few that actually guide students through the process but sometimes I get so frustrated when I frequently end up on purported educational sites that are full of: ads, links to print a black and white outline of a cartoon character or anything else, games that test knowledge instead of teach it.
Children's educational websites need to be focused on one thing. Learning. There should be no other distractions on the site and if absolutely necessary, links to things not related to the learning part should be unobtrusive and hidden in a corner. Even PBS Kids has a prominent print button on almost every activity and when I turn on my printer I find that there is a cue of 10 things to be printed from my kids, most were probably by accident by my 2 1/2 year old while her big brother helps her with Elmo.
Scouring through the web there are lots of wonderful things you could use if it happens to fit into what you are or could be doing. The problem arises when you are looking for something specific and only manage to find a printable word search or a hangman game.
Searching for information appropriate for younger audiences is also very tricky. The advanced searches and the dedicated searches and the hidden searches we tried out are great for doing hard core research. Third graders on the other hand need something they can read and understand. Google advanced search has a reading level filter for basic, intermediate and advance but I don't think it's always very accurate. I was happy to find SweetSearch, a dedicated search engine for students from Dulcinea Media. Check out their search and services.
Speaking of younger audiences, I was pretty disappointed with Google forms and even Zoho Creator and their inability to have any decent layout and design. Vertical block layout and no ability to put a graphic right where you need it. The form tools are very limited. Younger audiences should be presented with forms one question or idea at a time with a next button to go to continue. The design of the form/questions needs to allow for graphics to aid in understanding. I wish I had time to show you an example of what I'm thinking. Maybe down the road.