What do the poems "To Sylvia" by Leopardi and "We are Seven" by Wordsworth have in common in terms of writing style, content, and form?

Both these poems are concerned with the same two major themes: childhood, or youth, and premature death. However, the attitudes of the poems towards these themes are fairly disparate. This can be discerned not only from the content, but also from the rhyme-schemes, tone, and mood of the poems. 
Leopardi's "To Sylvia" is an elegy lamenting the premature death of a girl, Sylvia, "ere the grass was touched with winter's frost". It is composed of six-line stanzas in the Romantic style, and its mood is melancholy. The narrator does describe the "bright color" of life as a child--it is evident that he and Sylvia had grown up together--but to him, this speaks only of "treachery" in nature, because Sylvia was taken by "fell disease" before her time. To this narrator, then, it only increases his "bitterness" to remember the wonder of youth with Sylvia, knowing that she was never able to fulfil her potential--"the flower of thy days thy never did'st see." 
Wordsworth's "We Are Seven" takes a quite different approach in its discussion of children and death. It discusses a meeting between the narrator and a cottage girl, aged eight, who insists that "we are seven" (of herself and her siblings), even though two of their number lie in the churchyard. The tone is far lighter than that of Leopardi's poem, indicated immediately by the structure: the four-line stanzas, in abab rhyming couplets, do not set the scene for a lament or elegy. 
As in "To Sylvia", the poem reflects on the fact that children know nothing of what is to come in terms of what death means--"A simple child...what should it know of death?" The subject of death in Wordsworth's poem, however, is treated as, rather than a tragedy, a sad but simple fact of life. The child's proximity with death is indicated as she describes how she sits by the graves of her siblings to knit her stockings, whose "graves are green". Though the narrator insists "They are dead, those two are dead! Their spirits are in Heaven!" the little girl still feels she is one of seven siblings, and is not troubled by the fact that two are no longer on earth -- "O Master, we are seven!" 
There is a certain sadness in the fact that the child here does not understand what death really means, but if the narrator in "To Sylvia" seems to have brought his life to a halt in a mire of bitterness because of premature death, the family in "We Are Seven" seem to approach death quite differently, whether or not they fully understand it. To them, it is accepted as a natural part of living, and of being a family. In both poems, premature death is saddening, and children are portrayed as innocent of its true meaning, but the effect of the deaths in each case is quite dissimilar. 
 
https://americanliterature.com/author/giacomo-leopardi/poem/to-sylvia

https://www.bartleby.com/145/ww124.html