I had a tough time with a sling with a young baby past newborn. I loved my front pack, but once dd hit about 16 lbs it would kill my back. If you go to www.thebabywearer.com you can find reviews of different frontpacks and carriers. I ended up getting a new frontpack that had the extra strap around the waist and that made all the difference in carrying dd. This is the one I got http://www.babytrekker.com/. I like it when it is being used, but it is kind of bulky when not in use. It does all wrap together into its own bag which is nice.
Now that dd is walking/running, I can use my sling again. She hates the front pack (I haven't used it since Dec) b/c it is too restrictive. But with the sling I can put her on my hip and put the sling around her behind/back and it allows me to still keep my hand on her to help with my back, but also gives me a bit more arm freedom. If you go to this link http://www.mayawrap.com/ you can see the mom on the far left is holding her toddler like I do mine. I rarely use it b/c she wants to walk and run like her big brother, but it has been handy a few times. DD is about 21 lbs.
HTH,Kimberly with 33 m/o ds and 20 m/o nursling dd
I didn't get my ring sling until my DD was 15 months old and a little over 20 pounds. I got it with the new baby in mind, but it turned out that it worked well for her, too. I carried her in the hip position, and she loved it. It was great for the times that she wanted to be held, but I was making dinner, vacuuming, or doing something else. I also took her to the mall in it a couple times so that I wouldn't have to mess with the stroller. I was able to let her walk a bit and then carry her a bit. I really wished I'd had it sooner. I even carried her in my mesh pouch sling (no rings) on my hip for a while today, and she's 30 pounds now. It was so much easier than carrying her in my arms.
I mostly use the slings for my 6-month-old now, and she's generally in the hip carry (occasionally kangaroo carry in front facing out). If she's sleepy, I'll pull the material up to her shoulders so that her arms are tucked in, and she'll snuggle in and fall asleep. A couple times I've put her on my back, but I don't feel as confident with her in that position.
The slings have been much more valuable to me than I thought they would be. I will warn you that if you haven't carried him in a sling before, he may not like it right away. The first times I put my girls in it, they fussed a little, so I made sure they were as comfortable as possible and then walked around doing stuff. After a couple minutes, they were distracted and having a great time. They soon learned that the sling was a nice place to be.
Hope that helps a bit!Stephanie w/ Megan (6/6/03) and Annie (11/10/04)