My youngest is 27 months and just went through having this "stomach virus" thing - it actually got her twice. The first time wasn't so bad - she only threw up once or twice and had just a little diarrhea. The second time really whopped her.
We took her to the doctor about it because we were worried about dehydration and all. They told us as long as she was willing to drink and eat, then those were good signs. They said to make sure when she cried that she had tears, and there was saliva in her mouth, and to monitor the diapers. They also said to stay away from dairy products because it was so hard to digest.
They also suggested getting pedialyte and or letting her have watered down gatorade. She was willing to drink water, and would periodically want goldfish crackers and/or saltines, but we didn't really push it much because anytime she would have something, she'd vomit.
She vomited a lot the first few days, and then maybe once or twice a day for about another 5 days - and then starting Friday, she started acting like her normal self and wanted to eat anything in sight! She had 5 chicken nuggets (and usually 3-4 is good for her).
(I actually had this virus. The Monday it "started", my tummy felt a little crummy, but Tuesday morning I woke up knowing that at some point I would be vomiting, it wasn't a question of "if" but "when". That was Tuesday and Wednesday. My other daughter woke up with it Thursday. While I only vomited really on Tuesday and Wednesday, my stomach felt crummy/queazy for another week or so after that. AND I needed lots of Pepcid when I did start eating more than just crackers and/or chicken noodle soup.)
Make sure you have some Mylicon on hand, and the tylenol and motrin will help with the fever and/or aches from having vomitted so much.
Just hoping that knowing what we went through might help you...good luck!! Hope your little one gets better soon!!