Halloween plans

Yes, we are planning Halloween. Around here you have to plan in advance epsecially when your dear children want to be something that isn't common and I have have to dig around for the pieces and as much as I like being crafty when it comes to custumes I am not the best. Well this is what the kids want to be - Avatar charaters from the cartoon version. My son has the complete set and watches them ALL the time. They (my DD7 and DS8) keep going back and forth who they want to be so I figures I just get robes and go from there. I was thinking short kimono robes but the one all around here are bright colorful or dark and pretty designes. No solids. :| or cheap.
so I found this at Wal-mart site they don't have Adult Small but do have Adult Medium in White. I could just dye them. I am also planning on getting sweats to wear underneath to match, so dye those too so it's all the same color?
http://www.walmart.com/ip/Womens-3-4-Sleeve-Terry-Robe/14239006

Just google cartoon Avaitar and you see all sorts of custumes for these characters.