• Mayo Clinic Minute: What to do if your child has an upset stomach

Kids are back in the classroom, and so are plenty of germs. A common back-to-school sickness is viral gastroenteritis, or stomach flu. It's an intestinal infection marked by watery diarrhea, abdominal cramps, nausea or vomiting, and sometimes fever.

Watch: The Mayo Clinic Minute

Journalists: Broadcast-quality video (0:58) is in the downloads at the end of this post. Please "Courtesy: Mayo Clinic News Network." Read the script.

If your child is showing symptoms of a stomach bug, such as vomiting or diarrhea, it's most likely viral gastroenteritis.

"We really want to make sure we're paying attention to their hydration," says Dr. Tina Ardon, a Mayo Clinic family medicine physician. "Even with a couple hours of vomiting or diarrhea, you can get dehydrated pretty quickly."

Dr. Ardon explains how parents can tell if their child is dehydrated.

Dr. Ardon says that you can determine dehydration by "monitoring someone's urine output, so less wet diapers in a baby or maybe less trips to the restroom for an older child," says Dr. Ardon.

To help improve hydration, without making the stomach more upset, Dr. Ardon suggests taking a sip or two of fluid every five to 10 minutes.

"When someone is having a lot of vomiting and diarrhea, you're not just losing fluids, you're losing electrolytes, as well. So, actually, oral rehydration solutions or therapies, which are available over-the-counter — there are a number of brand names available that patients can ask their physicians or their pharmacists about — … those are the best options that we can offer to our patients," says Dr. Ardon.

Another option would be a diluted juice or sports drink. However, Dr. Ardon says be cautious with the excess sugar content, which can worsen diarrhea.