Hi Sarah, I imagine these windows could be treated in the same way as conservatory roof blinds with Pleated blinds. These would be available in blackout options. Alternatively, shutters can be made to unusually shaped windows like these and I think they'd make a really stunning feature of such lovely shapes! Here's an example: Enjoy dressing these beautiful windows, Zoe

As it's for a children's room, why not do something based on old fashioned tent flaps. 2 triangles of lined fabric that slightly overlap, with small tie backs. You wouldn't need any gathering in the fabric and this would bring the cost down. You'd have to find a way of fixing the fabric at the top and on the diagonals, but I can't see that it would be terribly difficult. If you've got the space, you could even bring the curtain forward to create a play area between it and the window.

It all depends on the light and how you'll use the space and what style you're after - you can go for so many options, pleated blinds, Roman blinds, curtains, etc. Is that door the entrance door or a door to the garden? Sorry many questions, I hope this helps.

Blind would suit the window better as it’s small; look through fabrics together and ultimately let her choose but guide her towards a pattern (since walls are plain) that will last as a style but go for funky cord and cord knobs. In terms of colour contrast the walls - don’t match. For coral, you’d need green/blue..