"They can fly with their wings, a spaceship carries people in them so they can go to space. If their mommy calls them they can.
Spaceships have to go in landing spaces so they can count down from 10 to 1.
And, when the people want to land them they just have to pull the lever inside of them, and then it lands and when they are done they go back to their landing pads."
........ My (then) 4 yr old when asked to talk about "spaceships"
(Update October 2020.... wow... my kid turns 10 next month!! I actually remember this conversation and typing it into my bio 6 yrs ago)