What gifts can a birth/first mom give her birthchilds adoptive parents?

I feel like the adoptive parents of my birthchild think I’m too poor to give them anything, but I’m not!! Plus I just really like giving gifts. In the past I give them a card with a gift certificate inside. The adoptive parents have only once sent me a card for christmas. Other than that they only send me ONE professional picture at christmas time. Just the picture, no note or anything. Anyways, I feel like giving them a good gift would be a step towards a closer relationship. What should I give them?