What kind of cameras do most professional photographers use?

And is it a good idea to have to have speedlights when photograping young children and adults?

Canon SLR`s.

very pricy.

digital SLRs

of Canon or Nikon ...

As brands go, Canon is usually top of the line for sports/wildlife, with Nikon close behind.
As far as type, a digital SLR (DSLR) is the only way to go.
There are some who still use medium or even large-format film cameras for landscape, but they are being eclipsed by "digital backs" (medium-format digitals), or normal DSLR cameras and photo-stitching software.

Canons are very good!!!!

Canon

canon is what probably works good

i use pentax k100d

I use a Canon Rebel XTi, I love it, we are bff.

Well its either the Canon 1D mk3, Canon 1DS mk3 or Nikon D3 which in simpler terms, the best of both brands =)

Nikon. . .sometimes Canon

Depends on the professional, the job and the need of the end product.

You have three basic types:

35mm SLR/DSLR - sports, protraits, general photography work. Good print sizes from wallets to roughly 16x20.
Medium Format - high fashion, portraits, landscapes, still life. Can do quite large print sizes for advertising, magazine covers or 2 page spreads.
Large Format - landscapes and portraits where your end product will be quite large print or display.

The photographer will have information from the client to determine which camera format, film. accessories and equipment they will need.

Speedlights add an extra bit of versatility to the shoot a they provide a way to bounce flash or have off camera lighting accessible.

We can use flash or hotlights(lights that are always on) to acheive the results we are looking for.

Canon or Nikon

I believe preferrably a Nikon D3

when it comes to portraits, a lot of the "fashion photographers" use hasselblads, sinars, or mamiyas with digital backs.