The only way that i have been able to give my son medicine, before he now (thankfully) drinks out of the measuring cup, was to hold him on the floor and give it to him. The method is as follows:

place him on his back and straddle his chest so i am on my knees over him and put both of his hands above his head and hold his hands together with one of my hands. His arms prevented him from moving his head side to side.

use a syringe type measuring applicator to get it past his lips and give him very small amounts so he would swallow it. If i gave him too much he would spit it all out.

when the medecine is all in him, pick him up, wipe off any medecine that missed, and give him hugs to calm him down as he was usually upset by this time.

Believe me i know it is not real nice to force a child to take medicine like this but i find it much worse for his stubbbornness to keep him from getting better. they also learn what you are doing so by the second time it comes to give them a dose be prepared for the fit throwing and crying to start as soon as you try to give them any medecine.

Half-strength Gatorade is a good oral rehydration solution. Too much sugar in full-strength, it interefers with absoption of the water. Cheap. A flavor for almost everyone.

Here is another rehydration formula. It is better because it includes potassium.

Dr. Orient's Recipe

One teaspoon of "Lite Salt"(by Morton, 1/2 iodized potassium chloride, 1/2 sodium chloride in a blue cylinder),
1/3 teaspoon of baking soda (sodium bicarbonate),
10 teaspoons of table sugar (sucrose),
and one quart of water.

Another vote for the Pedilyte freezer pops. Anything frozen worked (and still works) for our kids, even just an ice cube. Ginger ale with a straw is another sick-time "treat" that gets them to drink, but not warm and flat like some people mentioned.

My wife & my daughter got severely dehydrated after a bout with the flu. On the same day. At the same time. I found my wife nearly unconcious on the floor early in the morning, called 911. As they were loading her into the ambulance, she was able to mumble that "the baby is sick too..." and sure enough, she was also severely dehydrated. The process of getting an IV into the baby took 10 tries, and I had to hold her while she screamed and begged them to stop. You don't want your kids to dehydrate.
But I found that forcing liquids does not work. Small, frozen bits of stuff, but on a constant basis, works well, Tiny amounts of liquid, given with a shot glass or dropper works too. Avoid over-sweet stuff, and don't give plain water. It never happened again.