Okay kiddo, the White House Military Office is a group of people who help the President of the United States with important military things. They work inside a big white building called the White House in Washington, D.C.
Think of it like this: when the President needs help with anything related to the military, like talking to other countries' leaders or making important decisions about our country's defense, these people are there to help him.
The White House Military Office is made up of different groups of people who all have special jobs. Some of the people help with flying the President around in a special airplane called Air Force One. Others help to plan important events and ceremonies that the President attends. And there are even people who work to protect the President and his family.
Overall, the White House Military Office is there to make sure that the President has everything he needs to do his job as the leader of our country, especially when it comes to military-related things.