The Ralts card shows when the couple moved in, and there's a frame of it on the wall during the couple's wedding.
Then, the Kirlia card shows that the couple finished unpacking, and had a baby. There's even a frame of the Kirlia beside the newborn.
On the Gardevoir card, the couple is now older. There's a frame in the back that shows a doodle–probably by the child–of them and Kirlia beside each other.
Kudos to Jiro Sasumo for his attention to detail!
by Efficient_Tap_8392