Kids wet the bed due to several reasons. First and foremost is the fact that the body of kids below six years is not fully developed and their bladder does not send the message to their brain to wake up and use the toilet. Night time dryness is the last of toilet training which kids learn late in life. In fact, before six years of age bedwetting is so common that it should not be treated as a problem unless the kid has begun to feel bad about it and it has begun to impinge on his/her self- image.
Kids also wet the bed when they drink lots of water or any other fluid just before bed time. Since they do not realize during sleep that they need to empty their bladder, they pass the urine on the bed. Sometimes kids can pass urine up to 2-3 times in the bed if they were given lots of fluids at bedtime. Limit fluid intake of your kid before 2-3 hours of bedtime in order to reduce bedwetting.
Sometimes, parents scold their kids so much that they get too nervous about bedwetting and hence urinate in the bed. Never scold your child to the extent that he/she begins to lose confidence and start getting nightmares about bedwetting. Gently wake him/her up once in the middle of the sleep and take him/her to the toilet. This will reduce the instances of bedwetting to a great extent.
Lastly, if you, as a child had the tendency of bedwetting then there are strong chances of your children reliving your experience. In a way, bedwetting is a genetic problem and passed on from one generation to another.