Einstein said, that imagination is more important than knowledge, as knowledge has an end and imagination doesn't. -Something to this affect.
I think its wonderful that you want to keep your children's imagination alive. Children live in the world of pictures more than not until about the age of 7 or 8 and so it's very important to keep this alive. The more they are allowed and fostered with this the more intelligent they become.
Ya know, one can easily look at everything as myth, even the things we see and feel and hear as the Indian religion sees it.
There are a lot of things you can do to keep it going. We have a nature table set up which is changed out for each season. On our walks we find things from nature to put on it, or sometimes when the kids are playing they find something they want to put there. I also put little magical things on it too, like little fairies and elves and gnomes that appear over night. Things I make or sometimes buy. When the children see them in the morning they are just taken with delight. And we say, "looks like the house fairies have gifted us again with another little surprise, they must be very busy." I keep it on the simple side and as natural as I can. For the spring nature table I laid out silky light green and pink cloth and put down moss and made a cave from clay and put blue cloth to look like a river running out of the cave and then put a clear glass shallow bowl and laid light blue stones on the bottom of it and put water in it and then put little flower buds made of felt and the little fairies and gnomes some bought, some made. I also put a small vase with twigs from the flowering tree. I left the sleeping seed children from the winter scene bc some seeds are still sleeping in the earth. The seed children are little brown felt dolls about 4".
There are all kinds of lovely books to read, the Tiptoes Lightly Series are very nice. Puck the Gnome is a good one. Although these might be a bit old for a 5 year old. Pico the gnome is a nice one for 5.
Keeping the environment magical means a lot, simple, but soft and magical. Colored silks are a great way to decorate or to give the children to play with. They're expensive even when dying yourself, but you can get cotton. I have a perfect branch from a Dogwood tree I hung from the ceiling and then we can hang different things from it for the seasons or any way you want. We have a string of bees wax stars on ours and little white birds right now. Sometimes the children make things to hang on it.
Make fairy houses and make a fairy garden to put them in. Ask the fairies to visit with you and come close. Fairies like people that are respectful to mother earth. If the children ask why they can't see them as my 7 year old does then tell them it's because they live in a different world but also share our world. If they push for more info. tell them humans long ago use to be able to see them, but some humans didn't believe anymore for so long that their eyes became dim. Something along these lines. Some kids get afraid they will see them. I made a lovely little house for my granddaughter to put on her nature table for the house fairies, from the Tiptoes Lightly book they would talk about all the time. But when she received the fairy house she became afraid she'd actually see one. But after a while she was okay with it.
Celebrating the cyclic festivals of the year really make it enriching and fun for children. On summer solstice we make a fairy ring and I tell them a story about the fairy queen and how she will come close and we put honey in a sea shell which we leave over night for the fairy folk to celebrate. Of course the children can hardly sleep and as soon as they get up they go to see if the fairies ate up the honey. Which of course I cleaned out and put back where they put it in the fairy ring.
Like I say, there are so many things to keep this alive as it should be for any child. Unfortunately most children don't get this and instead are fed on awful characters from computer games and the like. Your children are at a perfect age for this magic. The book A Donsy of Gnomes is a delightful one. Drawing pictures for them is great too and having them draw as well. Writing and drawing a book about such is a nice thing to do and they'll love it. Any of Bestkow's books are lovely, which you can probably get at the library.
You may be interested in checking out Waldorf education sites and blogs, as you'll get all kinds of good ideas. Schooling from the heart, Today in Fairie School, Celebrating the Rythum of Life are just a few (hope I have the names right). Singing is so much a part of it too and verses and just having fun throughout the day. This will keep their livliness vibrant.
Have fun
I'm sure the Easter bunny is pink too.