I haven't worn my youngest, other than to demo briefly at babywearing meetings, for months. She's 3.5yrs old and is very interested in keeping up with her big sisters. She doesn't have time for being worn, she has places to GO! This past week we went on vacation to the beach. For the first time in years, my water sling didn't come with us, it wasn't going to be needed.
However, on the night we headed to the boardwalk to take in the Ferris Wheel and other rides, I grabbed my carrier as we were leaving, JUST in case someone got tired (my 5yr old still occasionally gets worn out). When we got there, both the 3 and 5yr olds had fallen asleep in the car. I put the carrier around my waist figuring it would just stay there. The youngest immediately said, "I want you to carry me on your back." You betcha kiddo. As long as you want. We had a nice walk, I only had to make sure I wasn't losing 2 kids in the crowd instead of 3, and she could remember that mommy is there when she needs me. Of course, after the rides she walked all the way back to the car, exhausted and whiny, but she "didn't need to be carried." You can't win them all.