What could cause a child to scream and cry during his sleep? How to help stop it?

How old is your kid? It could be either a nightmare or a night terror. Nightmares are often caused by several factors, like erratic change in sleeping pattern or anxiety. Lack of adequate sleep may also result in either of the two. Meanwhile, the latter is rarer and are seen in kids with ages 3-12 but can even be evident for toddlers as young as 18 months. Both have same causes. According to what I've read, it's best not to wake a child because it can make them feel all more confused and disoriented. Gently pat or rub his back/bottom and talk calmly. Make your kid feel he isn't all alone. To learn more about proper handling of nightmare/night terrors, check this link: http://www.whattoexpect.com/toddler-sleep-problems-night-terrors.aspx

It has a lot of reasons. It could be something about his physical state when sleeping--he isn't in a comfortable position or his diaper is irritating him. It may very well be he is having a dream that he feels uncomfortable, too. I suggest that whenever you put your child to sleep, make sure he is very comfortable, area is well ventilated and you can also put some calming background music.