Our german shepard runs laps in the backyard and has turned a big section into mud. I was thinking of putting decorative rock over it to solve the mud problem, but if possible, I'd like to put something that would be kid friendly too (our daughter (only kid) is 13 months and will be outside this summer and next year, etc)

Suggestions?
I am in Denver, if that matters.
Ideally, I'd like:
Cheap
looks good
kid friendly
dog friendly
low maintenance
cheap

THANKS in advance!