Thanks so much for the additional information.
The fact that they still have a lot of energy, have no other signs (other than the intermittent loose stool which might be secondary to parasites) and have a normal gum color are all very good signs.
It would be a little unusual for two pups to decide they don't like their new food but I suppose it's possible. I've seem some "good" eaters turn into pups who just aren't as interested in their food although it's not common for this breed. And, since I'm sure they're spending a great deal of energy running around and playing with each other, food might not be quite as high a priority in the scheme of things.
I've also seen pups develop mild fevers after receiving vaccinations
which causes them to have a decreased interest in food; however, they should not still be having this type of reaction five days later since it's usually within 24-36 hours after the shots are given.
I might offer them their old food. I might also mix some canned food
or a small amount of yogurt in the dry kibble
to "spice" it up a bit and tempt them.
I don't know if I'd offer boiled chicken
(since it's very bland) just yet although it's another option to try. If they eat it quite eagerly, then they may just not like the dry food as much.
But, it's hard to become too concerned since they aren't showing any other signs of illness at this time.