Space. It's all fun and games until you realize: MATH
Kids don't care that Pluto is no longer a planet, or that the moon landing may have been faked. They don't know who Richard Branson is, or that Neil deGrasse Tyson is basically the coolest dude in the universe right now.
They just know that stars are sparkly and the Earth spins around real fast and maybe, just maybe, the moon really is made of cheese. And that's OK for now. Let them run around yelling PEW! PEW! PEW! at imaginary aliens and counting to BLAST OFF in their cardboard rocket ships.
Because one day, in the not-too-distant future, they'll go to college. And some buzzkill admissions counselor will discourage them from taking astronomy because, "it's all physics and complex equations and blah blah blah."
Until then, you hop on that comet and ride, kid. Maybe swing by the moon and grab me a chunk of cheddar.