^^ forgot to add, you can do a double rod or for a cheaper look since it would be hidden, use one of these which is sold at target, walmart, etc. for like $10:
http://www.amazon.com/Levolor-13286-Double-Curtain--84-Inch/dp/B00004Z0JN/ref=sr_1_7?s=furniture&ie=UTF8&qid=1430763331&sr=1-7&keywords=basic+curtain+rod

You could do panels lined in blackout with a valance over them. That's what my girls have. Get blackout panels like this at PBK:
http://www.potterybarnkids.com/products/2321107/?catalogId=82&sku=2321107&bnrid=3518538&cm_ven=Google_PLA&cm_cat=Rugs_&_Windows&cm_pla=Window_Panels_&_Sheers&cm_ite=Dot_Blackout_Panel%2C_63%22%2C_Pink&kpid=2321107&srccode=cii_17588969&cpncode=37-42917517-2
they have tons of patterns and sizes.

Then for the valance you could do something like this (this is what one of my girls has):
https://www.etsy.com/listing/206699533/tie-up-valance-ready-to-ship?ref=sr_gallery_16&ga_search_query=tie+valance&ga_search_type=all&ga_view_type=gallery
Or just a standard valance:
https://www.etsy.com/listing/217408606/valance-window-valance-housewares-window?ref=sr_gallery_14&ga_search_query=window+valance&ga_search_type=all&ga_view_type=gallery again, in a coordinating fabric. You might even find your daughter's bedding has a matching valance or you can have one made from a sheet that goes with her bedding set.
etsy is great because you can have a valance made in coordinating fabric to match your DD's bedding. Just start a convo with one of the sellers. Or any local seamstress can do it too, it's not expensive.

Looking for ideas (and ideally links to pictures) of what to do for window treatments for my six year old daughter's room. There are nice white wood blinds already in place, and the room is light pink. I'd love to do something for room darkening. It will need to be outside mount (since the blinds are inside mount) or mounted outside the window, and should be fairly sturdy since they'll be opened and closed nearly daily. I think panels are too adult/formal looking. Would like to keep it to less than $250/window including installation and hardware. Can I do an outside mount Roman shade for that? And how sturdy are they?

Maybe something like this?
https://www.decorpad.com/photo.htm?photoId=100267

Thank you!