"You count four sons."
Translation:Quattuor filios numeras.
Quality adjective: an adjective that shows quality (good, bad, pretty, fast, etc.)
Quantity adjective: an adjective of number (some, forty, one, eight, half)
A quantity adjective goes directly before the noun it describes, while a quality adjective goes after the noun it describes.
Four is a quantity adjective. It shows how many sons. Because of this, "Quattuor" would go before the noun it describes - filios.
I hope that helped! :)