From about 3 years old the world of imaginative play and all its glorious possibilities opens up to your child. At this age children often move from playing alongside each other to actually playing together and developing friendships thanks to creative play. They'll have great fun acting out (and adapting) familiar fairy tales, pretending to cook, dressing up and role playing.
You can help by getting down on the floor and taking an active part in their games. Learning to involve another person in their imaginative worlds is key to forming friendships so even if you feel a bit silly being the troll, it really is worthwhile. You can also read books together that will spark their imagination through exciting, funny stories or expand their knowledge of fairy tales, different jobs and their favourite things.