Take a cardboard box and cut out 5-6 Valentine hearts. Make them big enough for young children to throw bean bags through. Decorate the box in a Valentines Day pattern and colors. Have the children take turns throwing bean bags in into the holes. Have a prize for the child who gets the most in with three throws and small prizes for all players.
If you don't have a box you can always draw hearts on a ground or wall with red or pink chalk and try to toss your bean bags into them instead.