Sleep associations can be a very important thing for helping your child fall asleep and stay asleep through the night. Sleep associations are what your child has or experiences in the few minutes before they nod off and fall asleep. For my daughter this is her nightlight, her stuffed animal, favorite blanket, the noise from the fan in the hall and her firm pillow. When sleep associations are a constant, they become habit and help her fall asleep.
Night wakefulness is a normal part of the sleep cycle, in between cycles people rouse a bit. Children gradually learn how to nod back off and basically sleep through the normal, brief periods of wakefulness. It can be an easier process if the child has all of their sleep associations throughout the night. When a child is falling asleep in their own space, with their sleep associations that are constant, such as a nightlight or white noise that plays all night, they are much better able to soothe themselves and continue sleeping during the wakefulness. If a child is held or rocked to sleep and then placed in bed, when they have normal night wakefulness, they are much more likely to fully wake and call out because overtime they are dependent on the rocking as a sleep association to be able to stay or fall asleep. If your children are waking and calling out often through the night, sleep associations may be part of the difficulty and are an easy thing to check.