Dog yard / Whelping pen

I have a fine dog house , kennels, whelping boxes. My problem is the yard. It's sand and a little grass. The mommas will go lay in the sand and then back to the pups. I'm sure not good for the pups and probably promotes parasites. Aggravating when pressure washing the floor and leaving sandy foot prints behind. We wash blankets twice a day when we have a litter of pups sand is no friend to a washing machine. My idea is a 6" to 8" bed of 3/4 gravle. Thought about the smaller pea gravel but if it sticks to mom it may end up in a pups belly. I was told by someone that their dogs avoid the gravel paths at their house.
ANY IDEAS WOULD BE APPRECIATED