Instructions
Load "The Sims 2" and enter into your Sim's neighborhood.
Hit "Ctl-Shift-C" to open the cheat window.
Type in "boolprop testingcheatsenabled true" and hit enter.
Enter your Sim's home and hold the shift key, then left-click on the baby and select the option "Make Selectable," which will make the baby disappear from the family list.
Left-click on the baby again and select "Make Selectable" again, allowing you to click on the baby's icon in the family list.
Left-click on the baby while it is selected from the family list and choose the option "Set Age" and then "Set To Birthday," then purchase a birthday cake and bring it to the baby, which will trigger the aging process.
Repeat step 6, using the birthday cake and selecting "Set To Birthday," to quickly age your Sim child into a teen or adult.