"Great parent would do anything for their son and I'm sorry I let you and your son down it's ... " (more) all my fault I'm sorry you're a great parent your son is really lucky to have you as a parent "
"I'm sorry I didn't get the costume to you my mother has been ill so I've been focusing ... " (more)on her more than sending out the costume I am very sorry and I feel horrible for not sending it "