My Beanie baby is (almost) back to normal. She isn't throwing up anymore, her glands aren't swollen and she's more active. She is slowly getting her appetite back. The fever is still showing up now and then but it's very low grade now (99-101) and usually only occurs when she's been playing hard.
I don't know exactly what she came down with, but I really hope your little ones never do!
Thank you everyone for all your concern and well wishes :-)