You can lie about the nutrition, but it is much harder to lie about the ingredients on a medication. The children's advil suspension lists the following ingredients:
artificial flavors, carboxymethylcellulose sodium, citric acid monohydrate, edetate disodium, FD&C red no. 40, glycerin, microcrystalline cellulose, polysorbate 80, purified water, sodium benzoate, sorbitol solution, sucrose, xanthan gum
The last time I looked, sucrose was "table sugar." Now there is more sorbitol in the solution than sugar, and sugar is listed as nearly the last ingredient, so I don't think it has a huge amount of carbs. Sorbitol is fairly low in glycemic index.
I suspect, worst case, it has a couple of grams of carbs.