Would kids respond differently to same medication if they dont have any congenital conditons?

Yes, no, possibly: Each medication has a unique molecular structure, designed to interact with specific tissues of the body in very stereotyped ways. It must nonetheless be noted that every person's unique makeup may cause them to respond in a variety of ways to different meds. TYPICALLY, there is a SMALL range of responses that MOST people exhibit, but it is possible to observe wild variation between two children.

They often do: The same medication is often used for different conditions, congenital or not, and there are often different responses that kids have in either case.