I've just transitioned baby #3 into her toddler bed . I have told each of my three kids on their first night in a bed that they are not to get out of bed unless mummy or daddy comes in to get them and we have had no problems with any of them coming out of their rooms. My eldest is 7 and still waits until I tell him he can come out lol!

How old is your DD2? Mine were aged 22 months (DS1) and 24 months (both DS2 and DD) when I put them into a bed and they were old enough to understand me when I explained that they needed to stay in bed.

Good luck!