What to do depends on where you are at in the course of the illness. The main thing you want to do is prevent your child from becoming dehydrated.
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For vomiting : If your child has just begun with vomiting, the best first step is to stop giving him all solids and most liquids. Your child will probably refuse to eat anyhow, so the solids part is easy. But after a few bouts of vomiting, he is likely to become fairly thirsty. Try to wait 45 minutes to an hour after the last episode of vomiting to give him something to drink.
Then start with clear liquids and small sips. If you offer your child eight ounces in a cup, he may drink it all (or a significant portion of it), and almost certainly it will come right back up. So start by offering little bits – on a spoon, in a medicine dropper, in the form of a soaked washcloth or a Popsicle. The goal is to get a teaspoon or so of liquid into your child every few minutes.
Once your child is able to tolerate small sips, you can slowly increase the amount. Offer a half ounce or an ounce at a time every several minutes. Gradually, you will get up to several ounces at a time, but this takes a few hours. Remember to stick with clear liquids such as water, watered-down juice, or rice water. Don’t give into your child’s pleas for large amounts of liquid or for milk. These are the two surefire ways to prolong the vomiting. If he refuses everything but milk, try soy milk or rice milk, but even so, dilute it with water. If all he will take (or all you have) is cow’s milk, water it down significantly.
For diarrhea : When your child has stopped vomiting (or if your child never vomited in the first place) and he is coping with only diarrhea, you want to rehydrate him as aggressively as possible. Excessive diarrhea can lead to dehydration when a child poops out more liquid than he takes in.
Clear liquids are the best for rehydration. You can give water, rice water, or any other clear liquid. Most juices exacerbate diarrhea, except for white grape juice, which can alleviate it. Rehydration drinks contain electrolytes to replace those that are lost during ongoing diarrhea. Unfortunately, these drinks are not safe if they are the only thing consumed for more than 24 hours. Also, some of these drinks are so unpalatable that they make kids throw up. If nothing else, you want to do your best to keep up with the fluid losses and not give something that is going to cause your child to lose more liquids.
When your child feels ready to start eating solids, give them to him. To help firm up the stool, give your child bland, constipating foods such as rice, pasta, crackers, or bananas. The old recommendation was to follow the BRAT Diet : bananas, rice, applesauce, and toast. But it turns out that any bland food is fine. If your child wants chicken, go for it. In fact, proteins are helpful in healing the intestine. Just stay away from spicy foods, sugary foods, and dairy products. Spicy foods will upset a relatively empty stomach. Sugar draws more water into the intestines, which can worsen diarrhea. And dairy products seem to exacerbate diarrhea almost immediately. If your child insists on milk, try soy or rice milk instead of cow’s milk, and dilute them if you can.
Some children with stomach flu will refuse to drink anything except water or watered-down juice, both of which offer almost ‘ no calories. If your child falls into this category, you may think he is becoming dehydrated because he will almost certainly have a diminished energy level. However, if he is urinating and the inside of his mouth is moist, he is not dehydrated. This confusing picture results from good liquid intake without nearly enough calories. To help boost your child’s energy, try to get some calories in him by giving juice or rice water with sugar added.
It is not uncommon for the diarrhea to last three to seven days (and sometimes longer) with gastroenteritis.