No Weldbond..it re-hydrates. First bit of moisture things will be popping off everywhere. Thinset is your best bet. I can't remember, but I think a couple people have done successful projects with kids and thinset

You can buy a tub of thinset already to go...easy peasy! Kinda like peanut butter, just spread it on.

I had 9-10 yr olds working with thin set in pastry bags, they did great

We started making stepping stones this morning with just over 50 kids - always on preformed cement stones (this is at least our 8th year of stepping stones at art camp) with broken up tile (same thicknesses)

We use mapei pre-mixed tile adhesive that comes in a tub.

first we trace the stones on butcher paper on the tables, and the kids work out their designs there. Then the helpers get the adhesive on the stones and the kids transfer their pieces over. Then the next day we grout. We have learned to do the grouting outside!

The "transfer" is difficult for my class of 3rd graders, who take great care with their designs and are often disappointed that they don't remember where the piece goes - so today we glued butcher paper onto the designs with Elmers (I put the glue on the paper first) and we will transfer the whole mosaic this way, using a wet sponge to loosen the elmers & paper once the design is pressed into the adhesive.

Then the next day we'll grout. So, that's 3 days & 3hour sessions, but we do lots of other art projects at the same time!

I hope you will post pictures of your finished project!