Start attaching-pebbles use hot glue,but if little hands are sticking them down, you can also use a super-strong double-sided tape, such as the type used to lay carpets. It’s entirely up to you how closely you’d like to pack those pebbles, as the grouting
Elf house on a tree! That would be cute in the garden, especially in the tree over grown with ivy. How about some battery tea lights in the windows during outdoor parties. I hear the fairies/elves whispering "home school project" in my ear.