Emotionally abusive ex keeps giving 2yr old ds food with cow milk protein in eg chocolate, cakes, biscuits, ice cream, even though he knows it gives him a severe upset tummy. Ds goes to ex's for day once every weekend and is on the toilet within the hour, for about an hour, when he returns. Ex insists it doesn't affect ds and I'm being deliberately difficult. I have even provided a shopping bag for ex with a variety of dairy free products, for him to take home and see what he likes to give ds. He returned all the shopping unused and said he didn't need my help. What, if anything can I do?