Use "must," "mustn't," "needn't," "have," "should," "shouldn't":
-- Well, kids, this is Kelly, your baby-sitter for the time we're away. You ... be nice to her. Dad and I are sorry we ... leave you for a month, but we really
-- Hi, you... be Sam, and this ... be the little Nancy.
-- Oh, you ... be so noisy. Come, Kelly, we ... show you around the house. You... do a lot of work. The only thing you ... do is feed them on time and look after them during the day.
-- ... I go shopping?
-- No, you ..., we have a housekeeper and a maid.
-- ...I wash up?
-- No, you..., you... do any work about the house.
-- What time ... I come in the morning?
-- You... come at 9 and stay till 5, but you... be late in the morning, and you ... allow Sam to stay out in the garden long You... be firm about it. If anything goes wrong, you... phone us
-- You... worry, I'll do my best.