If you are wondering still what to do with your young children for Valentine's Day there are a ton of great printables out there. These are the ones I will be doing with my children the next couple of days.Homeschool Creations (she also has a preschool pack)
Valentine Themed Math and Literacy Activities on Teachers Pay Teachers for free.
Over the Big Moon has an adorable pack that includes these activities.
Lawteedah has a big pack of printables including this cutting practice sheet
Two Teaching Mommies has a cute Sweethearts pack with lots of fun activities
File Folder Fun has some fun heart/valentine themed file folder games.
Musings of Me has a great printable pack of fun activities as well.