I have had some difficulties with rust-nightly so until this recent package was made available I couldn't build it to see how it had advanced. I am not sure exactly where the issue with rust was but Veloren uses the nightly version which is much more "cutting edge" and this may be part of the trouble. As opposed to minetest, I believe that any default options are fine and no fiddling is needed to get the most optimum result.
I happened across Veloren when it was little more than an idea and a blog. It is cool to see how much it has progressed in such a very short time. Since then I have played minetest quite a lot. First as Voxellands which no longer exists but its lineage was not known to me, then actual Minetest as singleplayer on my own box. The variety and interaction of a public minetest server adds a very substantial amount of depth to the game. Right now I have only spent significant time playing Veloren alone on my own box. The latest release of Veloren requires a login for the public server gameplay which I don't believe I have tried yet because I cannot recall any password I may have used there, so i hope I haven't. I can imagine that a public server will enhance gameplay too, I look forward to further advancements in this game's development. Its rather exciting to see. So far, it seems that the world is algorithmically created and many details are involved. There has been mention of mods or addons and other such concepts for making unique servers as is done with Minetest.
I think your kids will like the environment and detail and uniqueness as it is right now. The multi-player aspect you have covered with at least your kids playing together though you might find yourself on the game too. :D
UPDATE:
Rust is now built with llvm and seems to be much more consistently built, it might be that my troubles with rust-nightly will have ended.