Para aprender mais sobre os Tempos Verbais baixe agora o: Guia Grátis de Tempos Verbais em Inglês.
Ele contém um resumo bem estruturado para revisar os conceitos que você aprendeu na escola.
In fact the initial sentence should be "They visited us last year." Then, on Marcio suggestion "Did they visit us... (visit- the verb doesn´t take the "ed" in the end here, because of the particle '"Did").
So we think alike, with (...) I meant the rest of the sentence was like you pointed out. Indeed I expanded Marcio answer only because we could have English learners that might not have met the topic (or the information) of DID/DO not supressing the "ed" of verbs.