Complimentary planting for silver birch

[marshmallowpies]

We have a shrubbery at the bottom of the garden and I'm hoping to plant a silver birch at one end of it. I want to create a kind of den/children's play area in front of it, so I need some advice on some planting that could go around and under it - not so high that it encroaches on the birch and swamps it, but bushy enough that children could turn it into a bit of a den.
I also want to screen the garden fence as it's rather ugly.

The garden is west facing, and the other plants in the shrubbery at the moment are (in order from south to north), a ceanothus, a viburnum (tree rather than bush), a rowan and a laurel bush. The birch would go in the north-west corner.

As the planting needs to be child-friendly, nothing prickly or with poisonous berries, but all ideas welcome! I have thought of using willow to make a dome structure, but I'm not sure the space is quite big enough for that.

[TheNoodlesIncident]

Are you sure you want a silver birch? They don't really like being underplanted and anything shrubby right next to it is going to be competing for resources. If you really want a nice den then the dome structure would be nice, and you could plant a climber to scramble over it?

Alternatively you could plant a weeping tree that can be trained to weep a bit more and make a secret den underneath...? It depends how much space you have really

[funnyperson]

bluebells

something with dark evergreen leaves such as a clematis armandii or evergreen honeysuckle up the fence/wall behind the silver birch to help the trunk show off

otherwise I agree with the poster above, shrubs don't really thrive or look good under a silver birch: I think a playhouse on stilts might be good for a den under there, or perhaps one of those willow igloos?