The arch really is attractive, and I, too, would hate to see it all covered up. You might consider investing in arched movable shutters like those shown in the link below. Scroll down to see the arched treatments. My daughter has these in her house, which gets bright sun all afternoon. With the panels closed, it dims the room considerably against all sunlight coming in. This might be enough for your son's room.

Here is a link that might be useful: arched shutters

It is north-west facing, so it gets evening sun, and therefore I need a room-darkening window treatment to help my little one go asleep at bedtime.

I would wait to get into the house and find out whether you really need to cover the arched section in order for your child to sleep. The sun sets at 8:30 PM today, one of the longest days of the year. But before it sets, it lowers in the sky; covering the lower part of the window may be enough.

Thanks everyone for you suggestions so far.

Here the sun sets just after 9 pm, and my daughter is 2 yrs old and goes to bed around 7:30 (not to mention her afternoon nap too!) so room darkening is important.

What is the rule with curtain length? Either end at the sill or go right down to the floor?

Then I see a lovely little room like this and wonder if there are no such rules??

Here is a link that might be useful: link to nursery I like

Shutters are your best bet. I have an arched and an oval window, and the shutters are custom made to fit them.

I hear ya about the evening sun, our bedroom is on the NW side too, and the sun doesn't go down until after 9 from the windows.

Shutters also keep out the heat and cold. They're expensive but worth it in the long run.

I'd go with shutters to fit also. They look great and covering the window with drapes takes so much away from such a pretty window.

I'm sure after a day/night or 2 your daughter will know that shutters closed means nite-nite even if it isn't pitch dark in her room.

Half price drapes makes black-out curtains in 108"+ lengths that are pretty affordable especially if you can catch a good sale at overstock or LNT.com and better if you can use a coupon code. HTH!

Here is a link that might be useful: example from Overstock

We have shutters in our current house now and do like them, but I'm ready for a change. (And for the sake of conformity, the other rooms that are on the front of the house as well will not have shutters.)

And let's say I did go with shutters in her room, the arched section of the shutters would be constantly closed anyway. I'm only 5'2" tall, so opening and closing the arched section up high several times a day (in the morning, in the afternoon after nap, before bed etc) just isn't going to happen. At least with curtains, when they are opened, the arched section will let in light as well. KWIM?

Another source to look is jcp.com. I noticed they have 3 blackout drapes (one in regular home WT section and 2 in clearance) in the longer length at low prices--if the colors work for you (always the challenge). If you can't find the grommet style that might be easier to pull open/shut on a daily basis, you might consider ring clips since they slide easily. If the hem looks too challenging to alter on rod pocket styles, you can cut off the top and rehem that quite easily.

IMHO they'll look best if you have them full length, rather than end at the window sill. It seems like that would really detract from the effect of the window. Even your inspiration pic, while really cute, seems to just miss the mark a bit on the curtains. They're ok I guess, but full-length would have been better--IMHO. You may have to get extra panels to give the fullness you want across the window when they're closed unless you go with custom widths. Good luck with your project!

Here is a link that might be useful: Clearance jcp.com blackout curtains

Do you have room for a cornice like this above the window?

You would be able to hide cellular or pleated shades underneath it during the day, either of which you could get in blackout fabric.

I need to do the same thing and have been trying to figure out if there will be enough room with the pitch of the roof to put up a curtain rod. I was planning on having some black out drapes made from some fabric I have.....

I have a hard time visualizing it working.

so glad you posted-I have the same problem-wonderful window-awful for guests who spend night over in our guest room/ office area -they are up at the crack of dawn due to sunlight-waa-not what I want-but cover the window? I don't know-isn't there a beautiful option somehow?...help?

Sorry to throw a wrench in the conversation, but I feel differently about arches.The photo above this post with the panels hung below the arch shorten the scale of the window (IMHO).I would place the rod at the top of the arch and hang the panels. When the panels are open, you will still see the arch. When closed, no blinding sun.

my dd has those same windows. while the arch is pretty, it's not practical. we got roman shades for her room w/blackout liner. if i want to show the arch, i just pull the shades all the way up. if you do drapery, do it to the floor (from above the top of the arch).

I have a number of arch windows in my house and I've treated them for the most part like any other window. When I first moved in I felt I needed them to show because they were pretty and different. After fighting the evening sun on our West facing windows, I gave up. The lovely lace sheers didn't cut the sun or the heat. I now have blackout curtain on the dining room window and a matchstick blind with liner on the kitchen. In my bedroom and bathroom, I have the same 2" blinds as the rest of the normal windows but heavy blinds for the blackout due to those being East facing windows.

My pic above is the guest/office room. I just can't hang a drape over the whole window length of my window tho I too have considered this option. I would love to see the top part of my window covered with a sunburst design in the half circle wooden shutter. Oak finish to match my woodwork.(!) I will get an estimate to consider $. Then I could enjoy the curved window effect day or night without having to cover it. Thanks for the many suggestions. You have started me in the right direction!

We had a roman shade put in the lower portion(the entire width of all the windows) and took matching fabric and "stretched" it over a flexible arch(sized from a template of the window arch). It was trimmed in wide piping (made out of the same fabric). The finished arch panel fit exactly into the arch and the piping helped "seal" the perimeter from sunlight leaking in. This can prob be done DIY if you are crafty.