POE documents for wife and son

Hello All,

My Wife and 4 yr old son will be travelling to US next weekend for first time on H4 visa and their POE will be at Philadelphia, also Visa is expiring on 30th Sept.

So wanted to know the List of Essential documents that they need to carry , including copy of my documents that might be required.

Also some inputs regarding the questions that might be asked at POE will be helpful.

Thanks in advance.