In essence, there's a reason. Number one, they may not be tired. That's an obvious reason, but we often overlook that. Number two, especially for toddlers, life is very exciting and life consists of playing, and napping does not equal playing. So, children may resist napping or going to sleep because they want to just play more. So, again, routine helps. If they are used to the routine, for example, after having a snack at 1 o'clock they have a nap...you can stick to that routine. Or, if they are in daycare and nap as a routine, it makes it a lot easier for them to stick to that habit. But some children, because of their personality types, like to push the buttons and try to see how far they can get away with it. So, if they protest and they can get away with it and parents give in, then why not protest next time and why not protest even more because it seems to be working?