- Disposable "training pants" cost, on average, three times as much as a diaper of the same brand.
- They leak. I don't care what the package promises; they leak far more and absorb far less than a diaper in the same size. Can anyone say "wedgie"?
- Even if your brand comes with some version of easy-tear-away and/or resealable sides–they aren't nearly as easily removed or replaced as a diaper. A soiled diaper can be removed and replaced in less than a minute without removing the child's socks, shoes or even pants fully. Putting on training pants requires full disrobing from the waist down. And lest you contend that a child can do it on their own–I would ask, can that child also disinfect the floor where they sat, urine-damp cheeks and all, to navigate the leg holes? No! So now you have to wash the floor and their rear–in an awkward, standing position probably, or flat on their back like you would have to anyway, were they wearing a diaper in the first place.
- A soiled diaper is easily bound up and secured into a tight little package by use of the tapes that moments before held the diaper on the child. Toss. Training pants require a plastic sack or some other device to contain the contents before disposal. Unless you want unleashed fecal matter sliding down the insides of your garbage sack/can.
- Contrary to marketing claims and popular belief, putting cartoon characters on your child's underwear, and/or calling a diaper underwear because it's harder for the parent to manipulate, will not motivate your child to use the toilet. If you want to motivate your child by putting "big-boy" or "big-girl" underwear on, then by all means–do so. But use real underwear. If the sensation of urine running down their legs doesn't deter them from wetting fairly quickly, then they probably aren't ready to potty train at all. Put the diaper back on and motivate them by enforcing–rigidly–rules like "babies can't eat gum" or go out in the back yard unsupervised, or some other big-kid privilege you think they are ready for. They'll want to lose the diaper and baby status fast.
I don't have a problem with mostly-potty-trained children using disposable underwear as a backup on long trips or overnight. Fine. Use them. But save yourselves a lot of money and trouble and keep them in diapers until the pull-up really is a back-up guard against inopportune accidents and not just an inferior diaper that somehow psychologically makes you feel better about your potty training efforts.