Depends on the type of thing/s they're into, their age and what you feel is appropriate.
Also, don't underestimate your children, they learn far faster that adults, adapt very quickly to new situations and quickly embrace concepts us oldies struggle with.
The new 'Elite: Dangerous' springs to mind: It's complicated, looks stunning, is vast and you DON'T get to shoot baddies in the face at point blank range with a shotgun. In a similar vein are the 'X' games, just avoid X Rebirth. They are space trading/exploration/combat games BTW.