What age is good to let young puppies out in pea gravel area. I want them to be able to go outside and play in early morning while it is still cool but I am worried they will eat the pea gravel and get blocked. These are four week old puppies. I normally have a big grassy area for them but we have redone the back yard and trying to get grass to grow. ( seed, fertilizer and peat moss) no place for puppies

Do you have a "grass mat" (the woven plastic kind used under x-pens, etc. at shows) or another easily rinsed patio rug or whatever that you could tack down and put an x-pen on, to keep them from accessing the gravel through?

I don't allow my puppies in my gravel yard until only my keepers are left; everyone else has gone to their new families. I don't want to be responsible for obstructions/surgury on others' pups. I can keep an eye on my own puppies and train them to leave the gravel alone if needed, but a whole litter is too many to monitor at once.

That's too young for pea gravel. They will eat it, and good luck with that !
Designate an area put some shavings down and let them play there. Easy clean up , and you can rake it up when they leave.