These and some kind of soft metal should work. A good hardware store should be able to figure out some metal plates that wouldn't need cut or have sharp edges.

But I don't know how kid friendly anything long lasting would be, depends on the ages I guess.

Artbeads.com

Frostproof has some nice permanent markers. The wire tags are on backorder but are supposed to be in this month. Plus they have oter types. you can email them at questions@frostproof.com.
RED

St Lawrence Nursery makes a nice solid brass label for about $2.50 each.

Hi Amm0810-
We recently had a thread here which talked about making labels out of simple aluminum pie-plate-foil, etc. See here
But, I just had another idea. What about art letter beads? Such as these seen here or here? And some stainless steel wire? It seems like it would fit right into the arts-and-crafts realm. I have not done it before, so IÂm not sure about photo-degradation, etc, but it seems like it would work. You might want to get ones which come with numbers too (for rootstocks, etc). I just may try it myself!
-Glenn

Make clay labels and hang them by a copper wire. You have to have access to a pottery kiln. Take a block of clay and slice off little slabs with a thin wire. Drill one or two holes in them. Then imprint/emboss each tree's name on one. After they dry, dip them in stain/glaze and immediately wipe the stain off, leaving some of the stain in the letters, then fire to make them hard as rock.

I decided to go ahead with the letter beads idea. See link below. -Glenn

Here is a link that might be useful: My new graft labels

Just a suggestion
I used those bought soft metal labels from a mail order or local source . I used the inexpensive engraver, I hang them from the tree or if on trellis or wire like for espalling(spelling) trees or grapes.
Otherwise I took aluminum siding scraps or even vinyl siding scraps. Used the smooth back part. Not the front wood grained part. Engraved and then took permanent marker. I have had mine for several years. Unfortunately some of them, got in a hurry, and didn't engrave some.
Thanks all
Jean