No one, not even adults sleeps through the night. We all go through sleep cycles and partially awake in the middle of the night. For adults about every 90-110 minutes, we partially awake as we go from one sleep cycle to the next. Most of the time we just roll over in our sleep and never realize we were awake. Sometimes, however, we do wake up and maybe drink a glass or water and use the bathroom, but we usually go right back to sleep without much trouble.
Babies do the same thing through out the night. Sleep cycles are usually 45-50 minutes and length and babies will partially awake and then go back to sleep. Some babies will cry-out when they partially awake, especially if they are a young baby (under 4 months old). It is important to not create sleep props for our children- such as rocking to sleep or nursing to sleep. Because if they awake in the middle of the night, they will expect you to perform one of these sleep props so they can sooth back to sleep. If we leave your babies alone, they will eventually learn how to self-sooth themselves to sleep. They might suck their thumb, grab a blankie, or some might hum themselves to sleep. But if we are quick to intervene in the middle of the night when they awake, they will never learn how to sooth themselves back to sleep.
It is important to take into consideration other factors for your child awaking in the night. Please check my post that lists the number of hours a baby should be able to sleep without needing a feeding. This information should be helpful for you to decide if your child is awaking out of hunger. Also make sure your baby is not to hot or cold when you put them to sleep. Temperature can cause a baby difficulty when returning to sleep after partially awaking in the night. They with realize they are too hot or cold but cannot do anything about it. So make sure your babies room is a good temperature and that you have enough cloths on your child. I also recommend putting your child in a very absorbent diaper for over night. If you do cloth diapers, try doing disposables at night. Some children will wake because they the wetness from their diaper makes them cold or uncomfortable.
My son’s sleep cycles are about every 45 minutes. When he was 2-4 months old. He would awake up at the 45 minute mark at almost every nap. He had difficulty transferring from one sleep cycle to the next. He would cry fro 5-15 minutes in the middle of his nap. I learned to let him cry and he would return to sleep. Once I started to unswaddle his left arm, he learned to suck on his fingers when he would wake early from a nap. This helped to sooth himself back to sleep and the crying greatly diminished in the middle of his naps. I also found if he would awake in the night, he would cry a little and then start sucking on his fingers and quickly fall back to sleep. I am glad I did not intervene and he learned how to self-sooth himself in between sleep cycles!
Also, I use disposables now. We use Luvs diapers during the day (they are cheaper) because they hold enough urine during the day, but don’t quite seem to hold enough fro 12 hours of sleep at night. We use Pamapers at night. These diapers are a blessing! They really hold a lot of urine and prevents leaks at night. Another thing we are currently doing is using size 3 diapers during the day and size 4 diapers at night. Going up a size for nighttime use can add some extra absorbency for the long nighttime ware.