Here are two reasons why your preschooler may be constipated. Plus, strategies that spell relief.

Constipation Cause: Poor Diet

"Poor diet is one of the most common causes of constipation," says Dr. Cochrane. "Maybe your children aren't drinking enough fluids or getting enough fiber." A lack of both fiber and fluid means things start to back up. Why? High-fiber foods help keep fluids in the stools, and fluids help move things through by keeping those stools soft and passable.

How to Treat: Fluid & Fiber

Encourage your child to drink more fluids--water is best, but small amounts of juice and milk also help. "Typically the one time of year we see more constipation than others is during the hot months, so it's especially important to encourage fluids then," says Dr. Melvin Heyman, a pediatric gastroenterologist at the University of California San Francisco. Fruits and vegetables are great fiber choices. (Can't get your child to eat her veggies? Serve broccoli, peas, and other healthy options by adding them into casseroles, pastas and even pureeing them into soups. Also ask your child to help out when preparing meals--just don't give her sharp utensils. Kids are more willing to eat their food if they play an important part in making their own meals. Plus, click here for more ideas on how to turn your kids into veggie lovers.) If your child is a carb-lover, opt to serve him whole-wheat and whole-grain versions of his favorite sandwiches and muffins. But introduce new amounts of fiber-filled food slowly, as too much too fast can trigger abdominal pain.

Constipation Cause: Toilet-Training Woes

Do you have a preschooler who only goes poops in his diaper when she's hiding behind the couch? Or is she refusing to go at all? "Toilet training can play a role, too, especially when parents get into bad habits of pushing things too quickly or making things overly stressful," says Dr. Heyman.

How to Treat: Don't Make a Fuss

"Withholding behavior starts a vicious cycle," says Dr. Heyman. The more your child holds it, the harder and bigger the stools become, which means once they do pass, they can be painful. That creates an even bigger problem because painful movements can cause fissures, or splits in the anal area-and once they have a painful poop, kids remember it, and it possibly triggers a fear to go again. (Too much withholding can lead to encopresis, in which a hardened stool is blocking the system, but stool coming from above leaks out and around it and into a child's underwear.) To deal with the issue, play it cool in encouraging her to use the toilet for pooping. The less of a fuss you make about it, the less stress she'll feel and the more inclined she might be to revisit the toilet for a bowel movement when she is ready to. Also speak to your pediatrician, who will be able to offer more strategies on how to deal with the situation. If necessary, she may even refer you to a pediatric gastroenterologist.