The good news is a mouse could not eat enough "mouse bait," or "rat bait," to affect a dog, or cat, if the pet ingested the mouse. So I would not worry about a poisoning. He would have seen signs a few hours, after the mice were ingested, if poisoning was an issue.
However, dogs can pick up a bacterial infection from eating dead rodents. A gastrointestinal bacterial infection can cause bad breath odor as well.
You can try taking their temperature to see if they have a fever. Use a regular human thermometer. Put a little ky jelly, or vaseline, on the tip of the thermometer. Insert into the rectum about an inch. Wait three minutes or until the thermometer beeps. A normal temperature for a dog is 100-102.5 F. So, you can not tell if they have a fever just by feeling them with your hand as they run hotter than humans.
If they do have a fever, antibiotics will most likely be necessary to treat a bacterial infection.
If their temperatures are normal, I would monitor them for another 24 hours. If the lethargy, and bad breath, continues then they should see a vet to be examined to see if they have a bacterial infection.
I hope this helps.
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