Suggest Treatment For Persistent Vomiting

Hi my 4yr daughter just spewed yesterday, for no apparent reason, she wasn't sick or complaining of anything. She had a bowl of cereal for breakfast and a toast, 2 toast for lunch and four chocolate thin biscuits, once she started it was like she couldn't hold anything down, not even water. Then 4am this morning my 15yr son was doing the same. They didn't eat the same food.This morning she was hungry so I thought Id give her and ice block and she spewed that up to. what can she eat and what do you think cause this