Years ago I latched onto this idea from my cooperating teacher when I student-taught.
She secretly sent a letter home to parents in January. Inside it she sent a die-cut heart. She asked parents to fill the heart with words describing their child. (You could tweak it to be a favorite memory.) She also asked them to send in a baby/toddler picture of their child. She mounted the photos with the descriptions and people could try to guess who each student was.
I always include a current school picture under a flap with their name so that people can confirm their guesses.
It turns out so cute and it's up for conferences, so it gets a big audience!
I can't belive it's already time to start thinking about Valentine's Day...