Well...the problem being that the concept is a key part of the website, without this, there is no website...!
Your asking for ideas, but what is it that you want the website to do...other than be interactive of course? If is to aid learning and if so, what area (English, Science, Art, etc.), or is it for fun (and how will it be fun)? What is the target age group? Young kids have a VERY different needs (and attention levels) than those who are, say, just about to turn into teenagers. Are you focusing on boys or girls or both? This is actually very important.
Only once you are able to answer these questions...and a whole lot more... will you even be able to think of a website. Unfortunately coming up with a concept for a completely empty brief is completely impossible.
Obviously you feel there is a need for an interactive site for kids...where did this idea come from? Perhaps if you can identify this need, you can begin to answer some of these questions... and even coming up with the initial concept yourself.
Once you have this, perhaps you can bounce some ideas around here. It'll be much easier for people to suggest ideas once they know what it is you actually want to do.
WOW yeah that's a great idea...and there's loads out there to take inspiration from...Good think Alcutus.
I do rem tho, having one of those books and hadn't been written correctly and there was actually no way to end the book. You'd get locked in a loop going round and round the same few chapters over and over again...very annoying :(
Would be interesting to see how that would pan out as html...I like it =D
Have you ever seen a "Choose Your Own Adventure" book? It's basically a simple branching interface that lends itself well to HTML.
Write a unique story with 5-6 possible paths through it... then tell the story with no (or vet few words)... a picture book you can talk along with as you click.
Try to be focused, unique and charming... don't try to outdo "Kids TV Network" or be everything to everyone.
Remember that you're marketing to young moms, not 4 year old kids.