Why bring the women and children?

[Legolas]

It is yet another example of poor logical thinking by the writers- not thought out properly.

why did they not just stay there? He knew the Uruks would be going to helms deep and not Edoras!*Grrr* I don't get this guy!

The Uruks went there because they knew Theoden was fleeing to Helm's Deep. Had Theoden (or his people) not left Edoras, the Uruks would have gone to Edoras instead, plundering, sabotaging, and burning the entire town just like they had done in other settlements in Rohan. Edoras would've been especially susceptible to such an attack...they could've come at it from all sides, and it would be difficult to defend.

It would have been suicide for anyone to stay in Edoras.