Hello!
Are we allowed to change the children's lifestage as they become teens ?
I guess Elinoee meant turning to vampires, etc. (life state, not stage) So, the question is still open.
Glazey can have the last word when she pops in, but I'd say no because vampires have different lengths of life stages, don't they? There's the rule that you cannot extend life.
I actually answered this yesterday as life state, then realized it said life stage and deleted my response.
The only life states allowed are human and alien - I don't believe there is a way in game to turn your sim into an alien, so, no, there is no changing of life states.
If there is a way to change a human into an alien without cheats, let me know.