Sore stomach,projectile vomiting. Had chicken. What may be the reason?

Was dropping my son to school this morning when in the car, he complained of a 'sore stomach' (he hadn't had breakfast and was fine last night and when he got up ). We were literally around the corner from school and a minute after he mentioned his sore tummy, he projectile vomited in my car. It was quite massive and I took him to my parents to clean him up and my mum gave him dry biscuits and soup after he was settled. He hasn't vomited since but before dinner my daughter complained of a sore tummy and then when I picked her up, projectile vomited all over me (She was in the process of having dinner - chicken and chips and had 2 apples an hour before tea and some apple juice earlier in the afternoon ). She has since had two small vomits (both after I gave her a bit of soup) so I haven't given her anything but am just watching to see if she will vomit again. I'm not sure whether it is mild gastro that my son had this morning and my daughter has currently?