Daytime naps absolutely affect night sleep for babies! An overtired baby does not sleep well. An undertired baby does not sleep well. In other words, you want your baby getting just the right amount of daytime sleep, so they sleep well at night. To do this, it is important to have a sleep schedule set up. This way you know when your baby should nap throughout the day, and for how long. To get your baby on the ideal schedule, visit the sample schedules page, along with the ideal wake time page for a printable chart. I love this guide on sleep totals that your baby needs.