A sling, like this one:

http://www.mayawrap.com/

is light weight and reasonably priced. It can help you balance your load out with your pack in back and child in front like ironraven suggested.

My wife still uses her sling from time to time for our 2 1/2 year old. I have used it too and it makes carrying a lot easier, but a little hotter. We have tried different brands including one that my wife made and I think the Maya wrap one is the coolest.