You can still use your kit lens for the new born, but with some addition:
- a flash, as someone has stated, use it wisely, i mean: a *manual* flash with vari power.
- a set of radio transceiver to get the flash off-camera
- an umbrella, and light stand.
Use flash with 1/4 power or lower is harmless. Umbrella makes the light softer. Shot with kit lens at f5.6 still good.
You will need another lens to produce the shallow DOF - actually any lens from 2.8 and better. My personal choice is macro, to allow close focus on fingers, nails,.. new borns always facinating.
Manual focus is ok as long as you don't have to chase them. Otherwise get an AF lens for the long run.
Enjoy taking photos of children - challenging every time