If you have a Replicator dualstruder, you can put the attached s3g file on an SD card and print it.

Give them to your kid(s) so that they can practice addition.

Otherwise, you can:
- Merge the two STL files, using your preferred skein forge settings. The geometry is rendered properly located and centered to print on the Replicator, so don't do any manipulation in ReplicatorG (which could cause the geometry not to align). You don't need a raft. "Black" is the text, and "White" is the cards. Of course, you can use whatever colors you like. I'm leaning towards "glow in the dark" and "white",
- Edit the STL to change the problems, etc. You will need write.scad (elsewhere on thingiverse) to render the text. For example, you can generate multiplication problems instead of addition problems.

Disclaimer: there are tons of tiny cards, and (at least for me) not all of them stick, so you will want to watch the print and pull off any cards that come loose so that the remaining cards print cleanly. There are 81 cards, and I lost perhaps ten in printing. That's plenty to keep my son busy!