be careful with grammar tenses.(The Past continuous and Past Simple)
1. When Peter's mum(to Come)...... into his room, he (to watch)......the stars through the telescope.
2.I (to walk).......on the phone with Ann, when the films(to begin)

1When Peter's mum came into his room,he was watching the stars through the telescope2I was talking on the telephone with Ann,when the films began