Hello Gail, I'm Dr. Deb and will do my best to help you today.
I'm sorry that Stanley is having diarrhea but it's a good thing that he's still playful and not lethargic.
Loose stools in puppies this age are a fairly common occurrence and can be secondary to a variety of things such as internal parasites (a very common cause even if previously wormed), inflammatory bowel disease, dietary indiscretion or viral/bacterial infections to name a few possibilities.
If this were my case, the following is what I would recommend:
1. Discontinue all kibble but feed instead a bland diet of 1 part boiled chicken (or hamburg) and 4 parts of 20-minute white rice, 3-4 times a day. Once (if?) the stools return to normal, then gradually add his kibble into the bland food; this process should take about 7-10 days to transition from the bland diet to his regular dog food.
2. Over the counter bismuth subsalicylate (common in products such as Pepto Bismol) can be given as long as he's not vomiting and isn't currently taking any non-steroidal anti-inflammatory or steroid medication.
The dose would be 1 teaspoon per 10 lbs of body weight 2-3 times a day.
This drug can discolor the feces to a gray-black or greenish color though so this shouldn't concern you if it happens.
Pepto bismol should not be given to vomiting dogs since it contains salicylates (the active ingredient in Aspirin) which can irritate the stomach.
3. Start a daily probiotic such as Forti Flora which may be available from local pet or grain stores or can be purchased on the internet.
4. Encourage him to drink water or even pedialyte which is a good alternative since it can help to replace electrolytes lost with the looser stools.
It's possible that he'll need stronger anti-diarrhea drugs from your vet or he may need to be wormed but many pups will respond to the above suggestions within a short period of time.
If the stools persist in being loose and/or if he starts to vomit and/or if he becomes lethargic, then a vet visit may be prudent with a bagged stool sample in hand, if possible. As you probably know, these younger pups don't have the reserves that older dogs have and can deteriorate fairly rapidly so I don't usually advise owners to wait too long for them to be seen.
I hope this helps and that you see improvement soon. Deb