UPDATE Mother's Day was a no-brainer. I've talked to our son for the past week or so about it and what we ought to do for mom.
She loves Gerbers, so our son chose the colors. Also chose an awesome card and he wrote/scribbled on it to pretty it up. The bouquet was a little banged up by the time my wife got it on Sunday afternoon.
Our son proudly handed her the flowers when she came to pick him up from my place, followed by the card. Genuine excitement wouldn't be the word I'd use for my wife's reaction, but I guess if I were in her shoes, I'd have a hard time being happy in front of a person I'm disgusted with.
Nonetheless, I had no expectations. It was purely for our son's benefit and experience.
Speaking of his experience, this happened a few days ago: As he and I were loading up in the garage to head to daycare, he noticed the open garage of the neighbors across from us. They had two cars parked side-by-side and he asked why mommy is not parked with us. Then he teared up and said "I wish we lived in the same house, daddy." ...Heart-breaker.