Babysitting dilemma: Food

Ok so Ive baby sat my nephew since he was born. 8-9 hours a day for 5-6 days a week. I only charged them $20 a day. Now he is 2. My brother only buys a gallon or 2 of milk for me to give him with occasional cheese puffs or yogurt. I feed him breakfast, lunch, snacks, and i even give my brother left overs for dinner for my nephew sometimes. Im a sahm so i make them very good meals and snacks. I dont know how to bring it up to him that he either needs to pay me a little bit more since im feeing him from our items or buy him/bring more food. How would i bring it up? I dont want him to feel weird or something or sound rude. I feel bad for even asking since thats my nephew who i love dearly but it does make a difference in our budget.