when my boy is still a baby the longest i kept his food is overnite. now that he's grown bigger sometimes i still give him leftover foods from gatherings and events if i cant finish them on the day itself provided i kept them stored in the fridge not more than 3-4 days and the food has not turned bad. if your mother in law stored those food in the fridge it might not be that bad. but if she store it at room temperature with repeated heatings, then even i dont dare to eat it. you need to explain to her that babies tummies are delicate unlike us adults. giving them bad food might send them to an agonizing bouts of dioarrhea and even dehydration. why subject a baby to this risk? at this age they need to be fed with food full of fresh nutrients. repeated heatings destroyed whatever nutritional value the food is supposed to have. in order for a child to grow healthy you need to start them on healthy foods.