While flash is sometimes necessary, to add a bit of fill to shadows and add a little "pop" in drab light, it should be used more as the exception rather than the rule for more natural looking candid child and family portraits.
By turning off your flash, children (and adults) a lot of times will simply forget that you are even taking their picture. This lets them just do what they are doing so you can take some more candid documentary-style portraits.
Similarly, for romantic portraits of adults, turning off the flash helps keep the romantic feel to the portrait.
As I said before, sometimes flash is necessary and we will discuss that in later tips. But a lot of the time, flash is not necessary and simply gives a sterile look to pictures, kills the ambience, and adds harsh shadows and "flash spots" on the skin.
So get out there and try turning off you flash for your candid-style portraits, ambience shots, and romantic portraits.
Aloha from Maui, Kristin