Is this punishment that my brother and I received from our mom fair or too harsh?

I'm a 14 year old girl with two brothers, ages 12 and 9. Our youngest brother is always getting into our stuff without permission. Today, he came across a set of toy handcuffs that my brother owns and locked himself in them without looking for the key first. He came crying to my brother, who decided to leave him like that for a bit to teach him a lesson. Then he came to me; all I could do was laugh. I told him I couldn't help him, that I had no idea where Tommy kept the key. Around this time, our mom came in and he bawled to her about how we were being mean to him and look what we did, etc. Sorry, what "we" did? He was the one who got the cuffs and put them on without permission! But mom has always favored him when we have arguments and she wasn't hearing any of it. She had Tommy get the key and release him. Then, in order to teach us a lesson, she said, she handcuffed us together and took the key! We're supposed to stay like this until she feels we've learned something from this. WTH? Neither of us did anything, as far as I'm concerned. And while these are toy handcuffs, they're made of metal with no other release mechanism, so we're stuck like this until she decides otherwise. Is this fair? Personally, I think this is over the top, and I'm not exactly looking forward to trying to eat lunch like this!