DD went into her big bed at about two and a half. We needed the cot for the new baby. She hated it at first. She'd lie in the bed then the moment we finished her bedtime routine (story, songs) she'd cry to go back in the cot. In the end we achieved the move by getting some bedtime books all about moving into a big bed and reading them each night ( her favourite was My Own Big Bed by Mary Watson). Then she wanted to sleep in her bed... Then her cot... Then her bed... Every time I left the room she changed her mind! In the end I moved the cot next to the bed and told her to climb from one to the other as she liked. Not very safe and not my best parenting moment but it worked. She decided to stay in her bed after that and after a week or so she loved her big girl bed. :-)