Crap I still wear my PRE-SCHOOLER if he wants! LOL I have Joe who is 18 months and about 28 lbs or so and I sling him more than I do the pre-schooler of course, but he brings me the sling and says "up up up" When we go for walks I wear the sling and he walks until he gets tired then it is in the sling.
My pre-schooler who just turned 4 and is 50 (YES FIFTY) lbs goes in the sling when he gets really sick. He has RAD so when he gets sick he gets REALLY sick and he just wants to be held/cuddled and will ask to go in the sling. *sigh* my DH can carry him for longer than I can but I can go a little over an hour with him in the sling (just a ring/maya type sling). The sling also rocks with croup, walking up and down the street at 3 am...
Now of course slinging is a big no no for me, I am not even supposed to lift over 10 lbs. I do, of course as I have to lift Joe a few times a day but I do it as little as possible now.
I can't wait until the new baby and then I can sling again! ~