Using keywords, like "grandmother" and "son" (or probably son's name) will allow you to find those photos instantly! iPhoto is great at its job -- which is to organize and keep track of your photos for you, so you don't have to do the mind-numbing organizing manually like you do in Windows.
Don't go into the finder to look -- users are not meant to do anything in the library in finder. iPhoto keeps its library organized the way it wants so that your use of the app is easy. Let the app work for you and you will find it does a great job. Just use keywords when you import, rename your "roll" or "event" depending on what version you are using, and use Albums, smart albums, etc. to organize. Nothing could be easier.