I also know a way to get rid of the kid.
press SHIFT + CTRL + C to get the cheat bar up.
type in lowercase: testingcheatsenabled true
Note the space before the word 'true'
Next, hold down SHIFT and then left click on your so called child. It comes up a few options. Go to the one that is named 'Object' and then click on the option, 'delete it'
This method completely wipes the Sim from the game and every sim, pet, etc. has no recollection of the deleted sim, pet, etc. This does work with EVERY object/Sim/pet/food/dirty clothes/trees anything!! on your game. BE careful though! ONE YOU HAVE DELETED AN OBJECT, ETC YOU WILL NOT GET THEM BACK EVEN IF YOU UNDO!!
-Navaara6