In his letter, nine-year-old Dylan Harbin says he likes Trump very much and asks him to be his friend.
"My name is Dylan… but everybody calls me Pickle," Dylan's letter read. "I'm nine years old and you are my favorite president. I like you so much I had a birthday about you. My cake was the shape of your hat."
Dylan asked the US president several questions, like how old he is and how much money he had.
The boy also asked a question about the size of the White House. Sanders replied that there are 132 rooms in the US president's residence.
At the end, Dylan wrote that he didn't understand why people dislike Trump.
"You seem really nice. Can we be friends?" he asked Donald Trump in his letter.
Sanders replied that the US president would be "more than happy to be your friend."
The boy was also invited to an excursion around the White House.