Answer and Explanation:
This is the poem "Teenagers" by Pat Mora:
One day they disappear
into their rooms.
Doors and lips shut
and we become strangers
in our own home.
I pace the hall, hear whispers,
a code I knew but can't remember,
mouthed by mouths I taught to speak.
Years later the door opens.
I see faces I once held,
open as sunflowers in my hands. I see
familiar skin now stretched on long bodies
that move past me
glowing almost like pearls.
As was described in the question, a simile compares two different things with the help of "as" or "like". The purpose is to attribute a characteristic of one of those things to the other.
In the poem, the speaker is using a simile when she says, "open as sunflowers in my hands." Her children are now big, much bigger than she could have expected them to become in just a few years. It's as if she is surprised by the fact that they are no longer babies. They are grown, different, just like a flower is when it opens, when it ceases being just a bud.