Will I need to change my child's pants or clothes if my child has an accident while wearing a cotton training pant? Yes, if it is a full bladder-emptying urination. If it is a start-to-pee, then realize it and stop and go to the potty, then no, the trainer will fully contain it if it is a kind with a waterproof layer, such as Imse Vimse Training Pants. The amount of wetness matters.
When training you want the child to learn the natural consequences and needing to change the pants can be part of the learning process. It does catch a lot so these really help to keep the couch and the floor dry, and that is the point. Training pants are not diapers. They are for helping in teaching the child cause and effect, while providing some good protection.
Potty learning thoughts from Karen: Brain-connection-readiness comes in whenever that physical development happens. You can't rush the physical part just like you can't make the child's teeth grow in any faster. But the learning part - the understanding cause and effect - usually happens much earlier, often before age 2. So, it's up to you to figure out what you want to do for your child that fits his or her personal development and unique personality. Many kids can learn much earlier if given the opportunity to learn. But potty teaching is an inconvenient process in our society. Kids are wired to learn. Don't miss the window of opportunity when you see it beginning to occur. Wearing a training pant should be different than wearing a diaper. Thus, if a full pee accident happens in a trainer, that should not be the same thing as peeing in a diaper. So if the pants get a little damp, that is actually a good thing for the learning process.