Stomach flu

How long does it normally last with your toddlers my son came back from his aunts house with the stomach flu and tonight is the first night he’s thrown up because of it ( he apparently didn’t there) she also knew it had hit there home while he was with them my husband and our house wasn’t hit yet. Am I wrong for thinking that they should’ve have contained it to their home. Yes I know he’s my son and I should care for him when sick but I just don’t see the point of spreading it. I asked my husband to stop and pick up some things he could eat while having this and he only got Gatorade which I’m great full for but all we have that won’t upset his stomach is bananas which he won’t even eat.. ( I have no car and no way to get him stuff )