I allow the kids to play and get messy but I'm with mom a bit on this one. Clothing is expensive and allowing them to push trucks on their knees on bare pavement isn't something I'd do. Ripped clothes and sore knees lol. I'd either teach them a new way to push or we'd do a different activity.

When the backyard is too messy/wet, we play on the driveway with ride on toys, chalk, bubbles....things like that