I wonder if anyone can advise...
Our Dogue De Bordeaux puppy Dillan, is 13 weeks old and is normally full of mischief. On Friday we brought another puppy of the same breed aged 8 weeks called Stanley. Things got off to a good start. They were constantly playing and we never fussed one more than the other. Unfortunately these last two days, our older pup Dillan has become withdrawn. He doesn't fancy going out, sleeping more than usual and not eating much. He has vomitted twice but I did put that down to playing with Stanley after his dinner. This morning he turned his nose up at his breakfast. I am feeding them in separate rooms as they didn't like the other one sniffing at their bowl and barked aggressively.
I am worried.

It may be nothing, but I would see the vet.

Watch your dog closely over the next day. Look for any more signs of vomiting, loose stools, and lethargy. If any of these occur, please see your vet asap. At this age, both your puppies are susceptible to any number of viruses, so you need to keep a close watch on both of them. Please let us know how they both are doing.