Catherine, whether or not it is really necessary depends on the strength of your signal.

A simple splitter will degrade reception slightly at each of its outlets; an amplifier with multiple outlets can make up for the degradation.

I used to live in proximity to New York city, and was able to use a splitter to watch 3 tvs off my rooftop antenna.
Now I'm living in "the sticks" (Northern CT), and I had to buy an amplifier so as not to get "snowy" pictures.

I'm currently using a Channel Master 3044 amplifier. I paid about $45 at an electronics store, but through Ebay, you can probably get a new one for far less.

Thanks Tom!
I guess I'll try the splitter, and see if I need the amplifier. Thanks for your help!