PC space games that have educational value for kids include "Kerbal Space Program," "Universe Sandbox" and "NASA Kids Club," as of April 2015. "The Magic School Bus" has several different online games available, one of which deals with space.
"Kerbal Space Program" involves engineering a rocket ship to transport aliens into space. The rocket ship must be engineered correctly, otherwise it explodes. The game has elements of physics and engineering. It's under development, but multiple demo versions have been released.
"Universe Sandbox" is a virtual planetarium that has every known body in the solar system, along with information about each one. The simulator allows a player to manipulate aspects of the solar system, such as turning a planet into a black hole or giving a planet extra moons. The game has elements of astronomy and physics. It's also under development with multiple versions released.
"NASA Kids Club" has five difficulty levels, with multiple games for each difficulty. Games include Addition Blastoff, which uses math skills, and Flip Time, which uses memory skills. "NASA Kids Club" also has information on NASA missions and pictures.
"The Magic School Bus" game on Scholastic.com has multiple games available, including Space Chase. Space Chase is a quiz game that provides information about the planets and the sun.