Hi and welcome.
Light and plenty of it is the answer to good people photography and filming. Have you ever seen a film being shot outdoors and noticed the bank of lighting, even in bright daylight?
So, without good light, shooting people is tricky. The only way round it is to use flash or light the room up you are in. And that's not that expensive believe it or not as you can buy 500W lights from B&Q.
Pre-focussing helps. Press the shutter half way in the direction of the children, then press all the way when you you have the pic you want. Anticipation is the trick.
As for which model to go with, well, they both have the same sensor. The Canon IXUS 230 might be a tad better in low light, but if you want the longer zoom for zoo shots etc, then go for the Canon SX220.
And don't forget. Post processing is an important part of photography and should be used to sharpen and enhance pictures taken with your camera. If you don't have an imaging editor, then use the one in my signature below. There are http://ictpublish.com/pixlr/ to get you started. The most useful is the http://ictpublish.com/pixlr/Videoes/...06_Levels.html and for even more adjustment. The http://ictpublish.com/pixlr/Videoes/...07_Curves.html is a must (it's my favourite all-in-one adjuster). My Resize-Crop-Sharpen tutorial below, will get your pics ready for the internet or whatever
Last edited by Chris Cool; 11-09-12 at 12:16 PM.