Can't interrogate suspect arrested a child instead of the actual person lol!!!

I'm surprised it even let you arrest a child.

Are you using mods in your game ?

Did you already save the game ?

Then you will either need to roll back to an earlier save: http://sims4.crinrict.com/en/2014/09/save-games/#wiederherstellen

or maybe try if this method works in your case as well: http://sims4.crinrict.com/en/2016/01/arrested-suspect-cant-be-found-at-police-station/

Glad you found a workaround 🙂