Though especially for children’s liquid versions, a kosher version is nice, if one is available. Most people hold medicine doesn’t need a hecksher. Vitamins are more of a shailoh since they are a food (and also, since vitamins are usually available with hecksher).
One has the issue with many non-prescription medicinces that they aren’t really effective or necessary, so is it okay to take what amounts to little more than a treff placebo.