I'm always surprised to see "big kids" in diapers. I don't have children myself, so maybe I am not really qualified to have an opinion, but I have asked (older people, that is) what they think about kids in diapers. The answers were unanimous. From 9 months to a year, potty training should be in place. By a year and a half a kid should be able to tell when to go. Yet a few days ago I saw three-year-olds in diapers. The parents are intelligent. The children are too, they talk and understand a lot.
I know from my mother, that my brother and I were pretty well trained at one year and a bit. A male friend said, after a year and a half his daughter was trained. My colleague said, at 9 months she saw her daughter in the sandbox looking down disgustedly at her diapers and she knew it was time to potty train her. Her son started later.
Of course promoting kids in diapers will boost the diaper business (and fill up the garbage dumps).