weak, rickety person, emaciated
尩 centers on physical frailty: a weak, emaciated, or rickety person whose body is bent or unsteady.
尩 is thought to combine 尢 (a person with bent legs) with 王, which may have contributed a sound or served as a distinguishing mark. The exact historical development is uncertain.
The lower part 儿 suggests a person's legs, and the upper part 王 looks like a heavy weight pressing down. Imagine a rickety person whose weak legs bend under a heavy crown-like burden.
For オウ, picture a weak person trying to say 'Ouch!' but only managing a feeble 'Ow...' as their legs give way: Ow -> オウ.