Translation:The children want to build a thing, but certainly not a building!
I don't normally say 'kids', ie it is not part of my English. Children should be totally acceptable.
"Children" is not only accepted, it is actually the word used in the correct answer given at the head of this comments page. I always use "children" to translate "geknaboj", and it has never been marked as wrong. I am surprised to hear that you used it and apparently it was marked wrong.