I would think that shoe boxes would be fine! Just a think layer of concrete, then as it is setting up they can write their name in it. What will be done with the bricks? Remember, a shoe box is much larger than brick, more like a stepping stone.

Go to your deli in your town and see if you can get some carry out plastic box .If you use sb you might have leakage in less you line it with plastic .Try one and see !!

Make sure they wear plastic gloves, concrete is very caustic. This will make a huge mess so needs to be done outside and wear old clothes. Plastic containers are better because the concrete might push out the sides of a box if it's too wet.

After they finish decorating the blocks they should seal them in a plastic bag and set aside for three days to cure. Any bag from the store will work.

Sounds like a wonderful idea! Maybe let them add stuff like a mosaic..keys/marbles, etc.

Be careful mixing, or if you are using premixed, when you add the water, dust is harmful to breathe, mix by pulling toward you in smooth even motion, I use a hoe. And when you think it is well mixed, mix it some more because if it is not well mixed the blocks may not stay together or corners break off. shoebox with plastic lining it would keep cardboard from soaking up the moisture & making a mess. Might run it past the mosaic or concrete forums for more ideas. How many kids to do you that would be doing it? Might get expensive.Maybe by shoe boxes you mean plastic ones?I think you have to rub them with Vaseline so you can get the concrete out, they would be pretty heavy so might drop on their toes. A place that sells food containers to cafes might have some disposable containers a little smaller & easier to work with. Jan

Mixing concrete needs to be done by adults and wear a mask because the breathing the dust is harmful.

I've found that containers with thin walls like a cardboard shoe box won't hold concrete well even if you line it with plastic because the sides will slump out as you pack the mix in unless you have a lot of skill with controlling the moisture in the mix.

Plastic would be better. I don't know what kind of budget you have, but my grocery store carries Glad brand plastic containers very reasonably. I'm thinking in the 3 for $2 range for a sandwich-sized container, which is the size I'd recommend. Or maybe you have a dollar store nearby that you could scour for deals? Just remember the stuff is HEAVY. Shoe boxes would be a little on the big side, IMO, unless you're talking about baby shoes, and I agree with those who said cardboard would need to be lined with plastic that won't leak.

If you use plastic as your form, spray the inside with Pam before filling with concrete.

Also, this is VERY important: Use mortar mix, not regular concrete mix. The aggregate in mortar mix is sand which leaves it smooth enough for carving names. Concrete mix has gravel and won't work. As others have mentioned, you also want to be careful not to add too much water. You'll want to be able to shape it into a ball in your hand and have it hold. If it falls apart when you lightly press it, add a little more water, but you don't want it drippy like cake batter. Think sugar cookie dough instead.

Once you pack it into your molds, water may collect on the top while the kids are trying to carve their names. Don't fret that. Just lay a paper towel on top and let it soak up for a minute.

Also, depending on the age of your kids, you might want to have a metal file or coarse sandpaper handy, so you can smooth down the top edge a bit after you unmold it. Concrete can be really sharp, but will take well to gently filing if it's only a few days old.

As others have said, you'll want to be able to cover your bricks with plastic and let them cure for at least 2 days before unmolding and letting the kids take home. So make sure to give yourself enough time.

Not sure what I'm forgetting.....I love, love, love working with concrete and mortar and think this will be a fun project for your kids. I'd recommend you giving it a shot on your own first then make adjustments from there. Careful, though, as you might get hooked! LOL I started out with stepping stones and am now making sculptures using metal armature (you can check them out on my blog below for kicks).

Here is a link that might be useful: Loribees Garden Blog

I did this a few years back but had each one bring a cake or pie pan. This way it didn't take so much cement. The shoe box would work but some are kind of big. Why couldn't you use some of those disposable pans made for small loaves of bread and that way you could get them at Walmart or the Dollar Store cheap. The pie pans worked great for us and they could write on them or even decorate them with little glass stones or really anything. I had a little concrete mixer that looked like a 5 gallon bucket with a lid and you were supposed to make sure the lid was fastened and that way you could roll the bucket on the ground and the concrete came out great. My husband mixed all of the concrete and there was plenty for everyone. Ours turned out like stepping stones but it would work in the little pans and be uniform in size.

"Why couldn't you use some of those disposable pans made for small loaves of bread"

Ooh, great idea! I've used those disposable foil cake pans as molds for stepping stones and they worked great. Do spray the inside with a little bit of Pam though, as it helps them pop right out.