My 3 year old nephew refuses to sit on the potty. We have tried everything for the last 2 years. Btw I'm fostering him and his brother so they live with us. He has sat on the potty before and used it but now refuses we have made it fun and played games while on potty I've literally tried everything now he will throw a huge fit of any mention of him using the toilet. Idk what to do please any advice.