'Childhood cannot be postponed", Children need to enjoy their childhood phases as they come. There is no one room that fits all phases. Yet there are solutions to have a room concept that evolves with your child. So it is not about furniture. It is a concept. It is about your children. Accept that their room needs to evolve with them and let them live the moment.
Children in their comfort zone are more creative, more positive and less cranky.
Give your children a room and make it theirs.