A great poem for use at Church of Jesus Christ of Latter-Day Saints baptisms is "Washed Clean," written by church president Boyd K. Packer. The poem can be found in his April 1997 General Conference address. One stanza of the poem reads, "He taught that justice will be stayed / Till mercy's claim be heard. / If we repent and are baptized / And live by every word."
While the original poem "Washed Clean" is quite lengthy at 12 stanzas, using only one stanza from within the original poem results in a shorter poem that can still stand alone. The last stanza says, "If we could only understand / All we have heard and seen, / We'd know there is no greater gift / Than those two words—'Washed clean!'" This poem is appropriate for a child's or adult's baptism.
Another poem that is appropriate for a Mormon baptism is "Baptism," which can be found in the October 1974 edition of Friend magazine. The poem talks about how John the Baptist felt when he was being baptized by Jesus Christ and compares that to how a child is now being baptized in the same manner.
The poem "My Baptism," located in the May 1996 copy of Friend magazine, is also a good choice at a child's baptism. It discusses priesthood power and how the child's father is performing the ordinance of baptism.