I like to schedule "dates" for birthday presents. I feel the memories you share are worth more than any physical gift you can give. I don't know the relationship with the 2 children you're giving gifts to, but $20.00 would be enough for a matinee movie and popcorn for two. And, starting an annual tradition has even more meaning.
I know you don't want to purchase gift cards, but a unique one is for Heifer International at Heifer.org. Heifer helps to end world hunger and save the earth. For $20, your gift recipient can go online and purchase a flock of chicks, ducks or geese that would be given to needy families. Or, they can learn about helping others and choose to save up other monies and purchase something more for needy families, such as a goat or sheep. Shares of more expensive animals can be purchased as well. Regardless, families are given the resources and training necessary to be self sustaining, a wonderful lesson for our children to learn.
Good luck with whatever you decide!