Obviously, the foundation of teaching Valentine's day to children is to introduce the meaning of love in general. There are a lot of underlying meanings of love that you should uncover to the children. For example, only getting a small Valentine's gift is already an act of love. Another thing they need to know about Valentine is spending quality time with the family. In the family gathering, you can discuss their achievement at school or at the music course because a small appreciation is also a form of love.
Basically, the gift is not so much different from the ones you gave for Christmas. To decorate their bed, you can give them a pink penguin pillow. If Valentine's gift is usually chocolate, then, your boys must love video game controllers but edible. You can also give a book about love for their parents and a coloring book with a crafting kit Valentine's day edition. Since February is still chilly, you can give them heart pajamas. As Valentine's day is also an event where a family gathers, you can play this and give this board game about puzzles on the day.
Originally, the celebration of Valentine's day on February 14 was because of the day of the death of Saint Valentine, a Catholic priest who died because he married the blind daughter of the jailer who got cured of her blindness because of the priest. But, the official tradition of this day started after 200 years of his death. One of a poet in the Middle Ages linked his story with romance and love. The Valentine's cards too emerged from a tradition of sending love messages, with a picture of a cupid and some hearts and flowers.
Same as the Christmas day celebration, you still need to plan ahead of the celebration for Valentine's day. You can plan from the feast and the exchanging gifts to one and another. To do so, you can start buying gifts like flowers and chocolate days before February 14. You must include the Valentine cards, with your personal messages and handwriting. To fulfill the day too, you can cook together the meal for the feast and decorate the table as romantic as possible. This day is also great to propose the love of your life.