Yes, definitely. They used "design" as a translation in other sentences with "설계해요". Also, "The children plan a house" just sounds weird to me in English. I feel like the word "plan" is used more aptly with events, and "design" is used better for inanimate things.
I was thinking of some artsy project with children designing the house two people are standing in front of. Then it would not require the definite article with "children" -- or would it by the Korean reading?