I always reckon if you sip slowly then some of it will be absorbed before you throw up again. Little & often which is why ice cubes made out of full sugar squash work well, put in a freezer bag & bash into chips with a rolling pin for little ones.
WHO guidelines to quote back at your numpty friend. 
"WHO/UNICEF guidelines suggest ORT should begin at the first sign of diarrhea in order to prevent dehydration.
Babies are given ORT fluid from a dropper or a syringe. Infants under two are given a teaspoon of ORT fluid every one to two minutes. Older children and adults take sips from a cup. If the patient vomits, the carer waits a short time then persists with the ORT
A key element of ORT is that water is still absorbed from the gastrointestinal tract into the body, even with loss of fluid through diarrhea or vomiting. In the case of vomiting, WHO recommends a pause of 5–10 minutes, then continuing to slowly administer the fluid. In the case of diarrhea, WHO recommends giving children under two a quarter- to a half-cup of fluid following each loose bowel movement and older children a half- to a full cup. ORT is often given by parents or other family members in a home setting. ORT is also given by aid workers and health care workers in refugee camps, health clinics and hospital settings.
Mothers should remain with their children if at all possible. WHO recommends continuing breastfeeding and perhaps even re-lactating if circumstances realistically allow."
As a rough guide, one pint of warm water with a level teaspoon of salt & sugar diluted is more palatable than commercial ORT's and you can flavour with squash. If in doubt better to have a more dilute solution than none.
Hope all the little ones pick up soon x