Well, you can analyze the poem any way you want, poetry is open to everyone's interpretation. I believe that when the poet, Elizabeth Barrett Browning, compares love to "childhood's faith," she wants to show the innocence of that love. Children have blind faith in their parents, friends, etc. and can be quite naive, the way her love is as well. However, she can also be talking about the power of her love, because a child's faith is unbreakable - it is so strong, just as much as her love. Hope this helps!
