Well, if they're old enough to go in and out on their own, they're really old enough to do that cleaning themselves. I'd make it part of the "play outside" package. Here's the cleaner, here are some rags, clean everything that mud gets on.
But, they are 4 and 2.5 so getting the task done to any sort of standard is just not there yet. Ultimately I've got to come behind them and finish the job.
Not really complaining, just saying how it is. Kids are messy and lots of work. I love them so it's worth it!