Exactly what are they "cleaning"? If you mean straightening up clutter in, say, a playroom - I'd say, mom should declutter that room. I'm not saying throw away loved toys, I'm saying *put* them away somewhere not-accessible. If your 7 and 5 year old have that much clutter, *that* is a problem that mom has to handle. Tell them they can earn the toys back one by one (or two by two, for two children) by keeping their spaces neat.
On the other hand, if you were asking them to sweep the garage floor etc - just have them sweep an extra room.
ETA: I agree with stricter punishment if they did something dangerous. For example, if they climbed down the side of your house from the second floor - that's very dangerous, not just a "sweep an extra room" offense.