A. There are many things that can cause diarrhea at this age, including infections like Giardiasis.
If it has been going on for some time, you should likely see your Pediatrician, who can do stool cultures to check for parasites and bacterial infections.
A milk allergy, lactose intolerance, or other problem causing malabsorption, could also cause a toddler to have diarrhea. If he is very fussy, has greasy stools which are very foul smelling, or if he is not gaining weight well, then your Pediatrician might be more aggressive in looking for a medical cause for your child's loose stools.
Another very common cause of diarrhea at this age is simple Toddler's Diarrhea, which is often thought to be caused by drinking too much juice. Toddler's Diarrhea usually begins between the ages of 6 and 30 months and goes away by the time children are about 4 years old. They may have 2 to 6 watery stools each day, but otherwise seem well and are gaining weight normally.
Some things you can do if you think your child has Toddler's Diarrhea include:
- Limit or stop giving your child fruit juice, especially juices that are high in fructose or sorbital, like apple juice and pear juice. White grape juice can be a better option.
- Increase the amount of fat in his diet (talk to your Pediatrician about this though, so you don't end up giving your child too many high fat foods, which may not be healthy).
- Increase the amount of fiber in his diet (this recommendation can be confusing, since a high fiber diet is supposed to help kids who are constipated, but fiber seems to help many different kinds of gastrointestinal disorders).
Remember that the AAP recommends limiting fruit juice to just 4 to 6 ounces for children 1 to 6 years old. Even that may be too much for some children though, so a trial totally off juice might be helpful for children with Toddler's Diarrhea.
And it is important to work on this problem, since it may make it much more difficult to get him potty trained if he is having very loose stools.

