looking at buying new lens - sigma 24-70???

[nlp85]

Hi and thanks in advance for your opinions. I am currently looking for a new lens for my canon 500D, mainly for portraits. I have a canon 50mm 1.8 which i love for adults and newborns, but need something more suitable for young children that move quite quickly and frequently (alot of indoor/low light work).
My budget is a bit on the tight side ($800 and under preferably) and have been looking at the sigma 24-70mm 2.8. Has anyone got any opinions on this lens or suggestions of any other lens?

Am also using a speedlite 430ex 11 but am still l figuring it out

[PH005]

I have the 24-70 as my "walkabout" lens. Really nice. You will love it. Maybe the only thing to think about if going the Siggy, is that it takes a quite large filter, 82mm. My Hoya HD UV was pretty pricey.