It is very easy for a young kitten like that to get dehydrated and hypoglycemic. Depending on the level of dehydration, it is likely you will not be able to adequately treat that by giving him fluids orally. You can however try to improve his blood sugar if it is low and then get him in to see a vet as soon as possible. As long as he is able to swallow, you can give him a source of glucose orally. If you have any honey or syrup, give him some in an eyedropper or syringe. I would start with one dropperful and give it slowly so he has the chance to swallow it and not aspirate. This should help to improve his blood sugar if it is low, but he still needs to be seen by a veterinarian for further evaluation and treatment.
I hope this helps. Please let me know if you have any other questions.
We changed formula yesterday and his belly is very distended. . .probably needs to poop. Is there a way to help him do that?
If the mom cat is not stimulating his bowel movements, you can do it by taking a wet, warm soft cloth and gently rubbing the rectal area. It someitmes takes a few minutes to get the started, and after they do, it may take a few minutes of stimulation to complete it, but is usually works.
Monitor his stools and if he is not passing any or it is liquidy diarrhea, he may need veterinary help.