We Have A 4 Yr Old In Hospital With Vomiting

we have a 4 yr old in hospital with vomiting first, then very lethargic, now loose stools, 21 of them during the night. They had an awful time getting an IV going. Normally a very healthy child. They are calling it "roto one" or something that sounds like that. Is extremely dehydrated. I'm the great grandma waiting at home--sorry the info I gave is very inadequate.