LEDs for a robot costume

My kids are making a robot costume and I was wondering if anyone has any examples of some
simple LED projects that I could put together something quickly to augment their costume with some arduino
driven LED effects that runs off a 9V battery...

any ideas or examples?

thanks

Utilize a Arduino lilypad for this purpose and do not use the 9v batteries in place of that use a lithum power batteries ,the ones which are used in Mobile phones they are really sleek and slim so that sewing a small pocket for holding the batteries would not be a big think and will not look bad too and they come in various variations in terms of voltages like 3.3v or 4.5v or similar values that is simply pretty much for your implication.

About LED's i would suggest using SMD led's , They are the best for your implication because they will be nearly invisible and when they will light up will have a dramatic effect, while looking out for the battery choices look out for 4.5v' above 1000mAh or atleast this much.

Soldering SMT LEDs is not in any way easy... I'd recommend considering cannibalizing cheap LED xmas tree lights... (Wrong time of year to buy these though).

There are ready made SMD LED specifically for the LilyPad. Just use those.

http://www.sparkfun.com/search/results?term=lilypad&what=products

Might consider electroluminescent wire. Here's a pretty inexpensive option:

http://www.seeedstudio.com/depot/el-wire-2xaa-pocket-inverter-p-1103.html?cPath=207

I would also suggest that you implement BLINK M led's , these are LED's with virtually every existent color on earth in them and Plus the animations they provide are just outrageously staggering, i love these however a bit costly but you will love them(They have uC in them! ]:D)
Have a look on them by searching simply BLINK M on google they are provided by the company THINK-M