Make food interesting for him like cute sushi? Or get him involved in "making" his own food like mashed sweet potato and roll it like a dough, eat together with him? Or u can add some noodles into the porridge and let him get use to the texture of it first. Or maybe he is just going thru a phase, sometimes peer pressure works too. If he sees other children eating, he might wanna try himself, let him explore food with his hands, let him get messy.