Um, the creepiest thing about this, to me, is the basic idea that kids of that age would actually be aware of Valentines' Day, much less be exchanging cards! That didn't happen among my contemporaries until we hit our teens. I even found the notion of an 11-year-old Ginny Weasley sending the 12-year-old Harry Potter a Valentine in "Chamber of Secrets' a tad disturbing, though Harrys' mortified reaction was spot-on!
Cal me old-fashioned, but at that kind of age (how old is Lisa? Seven, eight?) all boys should think about girls is that they can't play football and they talk all the time, and all girls should think about boys is that they pick their noses in class and find farts hilarious!