We do Latin as a language study.
I feel they are getting much more out of learning it this way than just roots. I have the root books too. Honestly just learning words is boring.
My kids love to give me a sentence in Latin. I give them nouns, verbs, adjectives and prepositions, just like we do in Shurley Grammar.
I think by learning just root words the children miss out on so much. Also by learning LAtin then taking any of the Romance languages later they will find it so much easier. In fact with Latin they can go to the post office, or anywhere and "read" the Spanish, try it. My kids love to decipher all the Spanish and they havent' had any yet.
But this is coming from someone who took years of languages in high school and college. I am pretty biased.