This sort of behavior is not particularly unusual, but it is complicated for you because of the fact that you have twins. How old are the children? Based on the limited amount of information, my advice is to set sensible limits about their remaining in bed and, over time, the sleep cycle will become better established. When young children wake up at night they often are scared, so try to take measures (night light, open door, stuffed
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Animal shape vitamins with iron, etc.)that help them feel more secure.