New student teacher tomorrow. Got a Valentine's Day card from one of the students, what should I write?

I student teach in grade school and the students are precious.<br><br>Pro tip: Valentine's Day cards are not just for significant others.<br><br>This was part of a packet I got this morning, along with chocolate from each kid.<br><br>There is a "To [student teacher name] From [student name]" card where I can write a quick note, and I want to say something particularly nice, as this was very sweet of them.<br><br>What should I write?