What is the best otc remedy for a toddler's dry cough?

Honey: Honey has been shown to be a no worse cough suppressor than any otc medication. Of note, it's the brown honey that was used in the studies. If you want to try something off the shelf, Robitussin or even small dose Benadryl (diphenhydramine) might be helpful.

Honey, if over 12...: ...Months of age (some say 3 years): honey was tested against all major cough medicines and found to work better.