Some kids in Second Life do that, too; but the problem was that, although anyone can put a texture on a prim, it's another matter to make a card that opens, or plays a sound clip, or poofs out a shower of particles, or the other things that make cards special in Second Life®.
Well, now any kids can make a card with all that stuff, without needing to know how to write a single line of code!
You color the card, in your own Graphics program. (Or color it in Real Life, and scan it in.) You write the text, also in your graphics program. You add your own Sound Clip (or not, if you don't want one.) You find or make a texture for the particles that poof (or don't have any, if you're not a big particle fan.)
The card will be whatever you want it to be, made by your own hands, so you know that it'll be precious to the person you're giving it to, just like those hand-made cards are to Real Life family.
The Template is included, so putting it on the card in SL is a one-step process (instructions are included.) You don't have to worry about putting a different texture on each face, because the whole card uses just one Texture Sheet.
Delete the freebie bubble sound that's in the card for testing, and put any sound clip you want in there! Want to use a rude sound for your brother's birthday card, to make him laugh? You can do it! Want to use that "Apple of my Eye" sound clip that means so much to your Dad in his father's Day Card? You can do it!
Delete the freebie Dag's Bubble texture that's in the card, and put any texture you want in there, and it'll be used for the particles! Want the card to fill the air with pictures of your face, when it's opened? You can do it! Want to shower someone with their favorite cookie? You can do it!
This is your card, and you can make it be anything you want it to be!
Mod/No Copy/Transfer (so you can actually give it to the person it's for) L$75. On sale at Kick the Can, Livingtree (149, 130, 24) in the vendor with the Gift Boxes.