When you arrive at the orphanage, you should see some of Riddler's thugs standing in front of the entrance. One of them, when looked at with Detective Vision, should be highlighted green. If you haven't encountered one before, then there are minions of the Riddler and they are special. Interrogate them, like the one thug at the beginning of the game, and they will reveal the locations of some of Riddler's collectibles on your map.
The catch is that if there are other enemies around with Riddler's minion, you will need to defeat the others without defeating the minion. This can be a little challenging when you're concentrating on beating everyone up, as you might accidentally do the same with the minion. So, you need to be extra careful and pay attention to where the minion is at all times, making sure you vault over him or just stun him with your cape.
Once you've finished with the thugs, head inside the orphanage and you'll see Catwoman out in the open. Go up to her and press the button to rescue her, which prompts the Riddler to appear on the monitor. It seems that he has decided to forgo the traditional thug and make robots to do his bidding, which you now have to fight.
They are not that tough and in fact, they should be treated like normal unarmed thugs. This fight is special, in that, you can actually switch to Catwoman with L1 and fight with her if you please. As you build up your combo, you might see a button prompt to perform a Dual Takedown, which will combine the efforts of both Batman and Catwoman to destroy one of the robots, with the game switching you to that character. When all of the robots are downed, it's time to leave...well, one of you is leaving, as Catwoman has a bomb strapped to her neck and you'll need to do more of the Riddler's side missions to get keys to unlock the bomb.
