父母三月来美帮我们照顾刚生的孩子，现在想申请延期。正在考虑如何写申请信，什么样的理由容易获批准？
１。游了东岸， 西岸还没看。
２。孩子(5 months old)有medical condition that requires special treatment. We need grandparents to take care of our son so both of us can work to afford the expensive cost that is not covered by insurance. (Sadly, this is ture).
能否提供样本？sample letter.
最近延期形式怎样？
小弟多谢了！