Wouldn't it be great if your baby could just say "Yo Ma, I'm sleepy!" and you could just lay them down for their nap? Maybe in another universe where there are no dirty dishes or laundry, but here on earth it's a little different. The good news is your baby does have ways of telling you they are tired. It may just take a little trial and error for you and your baby to figure out their sleepy language.
Sleep cues are your baby's way of signaling they are ready to sleep. Before the age of four months you will use these to help your child go to sleep whenever they feel tired. After four months, you will use these to help you tweak your baby's new sleep schedule. As they get older you will be able to make special adjustments to their daily sleep schedule. (Maybe you had a big day at the zoo and a sleep cue can signal a early bedtime is in order!) Every child is different but eventually you will be able to speak your child's sleep language fluently.
Some examples of sleep cues are red eyes, rubbing eyes, pulling on ears, yawning, blank stares, sucking thumb/finger, less vocal, more vocal, pulling on hair, stretching, rubbing blankie, or droopy eyelids.
Now here is the tricky part- if you start to notice sleep cues, it may be too late! Ideally you want to already be preparing for your nap or bedtime when the sleep cues appear. (Think of sleep cues like hunger pangs. You want to be eating before you feel like you are starving right?) At first this might seem impossible, as sometimes they appear out of nowhere. But once you get the hang of things you can use sleep cues to help establish a schedule that fits your child and avoids any over-tiredness. Trying to put an over-tired child to sleep can be as disastrous as trying to put a child down that isn't tired at all. You want to find that sweet spot between awake and over tired using your sleep cue GPS.
An over-tired behavior in one child may be the same as a sleep cue for another child. (And some kids might not show any sleep cues and go straight to showing an over-tired behavior.) If your child is over-tired you might notice they seem upset, irritable, they may cry/scream, or start acting out. You may also notice your child doesn't seem tired at all and may seem to have lots of energy (I told you this was tricky!)
A great way to avoid any over-tiredness is to follow a consistent sleep schedule while being mindful of sleep cues. Sleep cues can be especially helpful when babies are learning how to self soothe! Watch the clock to see when your child tells you they are sleepy and try to adjust a little each day until you notice their sleep cues as you are already in their sleep routine. You may get so good your child never displays any sleep cues at all!