On March 7, 2021, Teresita Castillo de Diego died at the age of ten. The news spread around the world through the media and social networks, because the "Little Missionary Girl" had already stolen everyone's heart, and many people were closely following the progression of her illness. For her, to be a missionary was to suffer so that souls might know Jesus...And Teresita suffered so much! However, guided interiorly by Jesus and sustained by the deep faith of her parents, she offered her sufferings for priests and "so that many children may know Jesus and go to Heaven, to be happy forever and ever ." In this documentary entitled "Teresita, the Little Missionary," her parents, Eduardo Castillo and Teresa de Diego, her grandmother Teresa González Alió and her aunt Marta de Diego, as well as her best friend and some of her cousins speak about Teresita. Through their testimony we will discover that Teresita's mission to bring souls closer to Jesus is not over. And each of us will feel challenged by the generosity of this little missionary.