I'm not sure whether the Nobel prize-winning poet was referring to a specific experience where she witnessed children being neglected, or whether this poem came from a general compassion for the suffering of children. The poem in translation very clearly recognizes children as having a special ability to spread beauty and life. The translation I read was dedicated to lsaura Dinator. I haven't discovered who this person was yet; however, there seems to be a great deal of information out there about this poet if you care to take some time to search for it.
According to some bibliographers, this poem is one of many which have gained popularity since the poet's death. Here is a quote (my edits) from http://www.educoas.org/Portal/bdigital
Poems such as “Piececitos de niño” [children’s little feet], “Miedo” [Fear], and “Apegado a mí” have gained an apparently permanent place within school curricula in Chile and Argentina. Despite the public’s enduring loyalty to the work that Mistral produced for use in the schools, scholars ... routinely overlook any part of the poet’s work that she has described as being directed towards an audience of women and children.