He owed me

My friend gave my son ten dollars on Thursday and he was so excited he could not wait to go to the store to buy a new toy. He was sick on Thursday so I told him that this Friday we would go to the store but yesterday he was still sick so I told him that we would go Saturday. When I came home from work he said that he was not sick anymore and he wanted to go to Wal-Mart. I told him I was tired and I did not want to go and he started crying and told me that he would have to wait to go tomorrow. He was so mad so to stop the crying we went to the store. He was looking for a toy worth $10 but when we are at the cashier it was $20. It was my fault I never checked the price so I paid for the toy anyway and told him he owed me $10.