As you can see, these aren’t playing cards but rather greeting cards– bigger and easier to handle. Pick up a box or two of pretty colorful ones at the dollar store just for this purpose.
Depending on age and ability, you might consider giving your child both the cards and a roll of tape, and let him or her figure out how to add stability to their building with the tape. An exercise in problem solving right along with the fun of building.
If sufficiently stable with the tape, the building can then double as a doll house for polly pocket people, or pebbles with faces painted on or little plastic superheroes- whatever. All in all, an entertaining and educational play activity.