"Ellos comen sándwiches en la playa."
Translation:They are eating sandwiches on the beach.
My answer was admittedly wrong because I omitted a word entirely, but the correct solution given was: "They've sandwiches on the beach." which means "They have sandwiches on the beach."
It's fine to say "We're having sandwiches for lunch" or something to that effect, but that is not the literal translation of "Ellos comen sándwiches en la playa."