Upset tummy

My 11 year old son has an upset tummy.  I texted the ex to explain and ask that son eats plain food to recover from upset.  He just came home looking sick and tells me he had sausages for lunch.  What? That means a day home from school.  Thankfully my mother is looking after his 13 year old sister tomorrow for "reporting to parents" day and can look after him too.  She normally says no to gastro related illness (and rightly so) but will look after him tomorrow. She asked if she should give kids spaghetti bolognese for dinner and I said no, we're avoiding heavy meals for the moment because of the vomiting!!!!!!!!