Why this mom buys Mother's Day cards she never sends

— -- A San Antonio, Texas, mom of three writes two Mother's Day cards each year, and then puts them in a shoe box in her closet.

The cards are for the mothers of her two adopted sons. They were adopted from China, and Jill Robbins has nowhere to send the cards. Still, she buys them and writes them each year, she wrote in a Facebook post that has struck a chord with adoptive parents everywhere.

"Mother's Day is very poignant for moms who come to parenthood through adoption,” she told ABC News. “I think a lot about their birth moms.”

Her boys, now 6 and 7, were adopted when they were 2 and 3 years old.

"I don't want for much but if I could have one wish, I would want my boys' birth mothers to know the babies they carried are safe and loved," Robbins wrote in her post. "Cherished. Thriving. Part of a family.

"So, I buy those cards every year. I write in them. Somewhere on the other side of the world there are two women who would probably give anything to get them.

“These women wonder where their babies are, I know they do. Although I don't know the circumstances that led to their decisions, I do wish them peace. I wish they could receive these cards I write every Mother's Day."

Robbins told ABC News she's "bothered by the lack of history about my kids before we showed up," referring to things like records or photos of first steps and words.

It's "cathartic” to write down her sons’ milestones, challenges and joys each year in the Mother's Day cards, she said.

Robbins has never re-read the cards after putting the in the box, she said, though she has been tempted to since her Facebook post. "Up until now, this had been a really private ritual for me. But I'll probably give the cards to the boys one day."