AF assist with 550EX?

The onboard flash on my Dreb will sometimes "strobe" when I'm trying to focus indoors. I realize this is normal, that it's trying to illuminate the subject to get focus. My small grandkids always think the picture has been taken when this happens and quit posing. Will using a 550EX, 420EX or equivilant flash override this behavior and use it's infrared (or whatever) to assist in focusing?

The 550EX / 420EX will use a red beam for focus assist. The red beam can be seen by naked eyes but it is less annoying.

Thanks nosquare2003. Looks like a new flash is in my future!

Yes, you will like it. The external flash:

1. have much more power than the built-in flash:
2. you can do bounce flash (or even off-camera flash) to avoid harsh shadow.
3. the 420EX/550EX helps to autofocus even in complete darkness (at a certain range).

If you can afford it, go for the 550EX, if you can. It will let you set FEC, 2nd curtain and FP sync, and you can even disable the flash (by setting it to TTL) so that you can use the AF assist lamp in places where the strobe flash assist would be annoying or frowned on, and you aren't allowed (or don't want) to use flash.

Thanks for the input guys!