as a teacher, i can tell you that some children (a little older, say 1.5-3 yrs) use throwing up as a manipulative gesture. they KNOW mummy will stay, come home or whatever BECAUSE they threw up.
if your helper cannot manage your child for a few hours by herself, you need a new helper. running home because your child cried so much he threw up is not going to help matters, it will just make it worse. he's not sick. he's angry. he needs to learn how to deal with that.
i had a child come to my playgroup for over a year. his helper used to carry him in a chinese sling, even when he was over 2 years old. this boy whined and cried and whinged constantly. finally, when i suggested that the helper stop carrying him in the sling and she followed through this boy changed completely. he became a happy, well-rounded boy almost overnight.
i am by no means suggesting that you should let your child cry if he is in pain or sad. but you are only reinforcing the behaviour if you cater to his every whim. you need to remember that you are the parent adn that he is just angry. my daughter has a TERRIBLE temper and there are times that i just have to let her have her tantrum. when she's finished, she either goes to sleep or says "sorry" and gives me a hug.
i wish you luck. sounds like you all have your hands full.