There's a few reasons. If toddlers are overtired, overstimulated, or ruling the roost, they will resist bedtime. Conversely, if they have napped until 5 p.m. they won't want to go to bed at 7:30 p.m. A child's resistance to bedtime shouldn't stop you from putting your toddler to bed at a proper time that prevents overtiredness and grumpiness the next day.