How about narrowing it down to one specific subject at first, try to get pre-orders (one time fee)? If successful, build it and then repeat. Once you have enough variation in content you can offer a subscription plan instead of individual pricing.

I see where you're coming from though, that you want to offer something that's greater than the sum of its parts, a single place where kids can go. But it's going to be difficult cracking that chicken/egg problem.