Before you can be a butterfly (http://www.thingiverse.com/thing:11369), you must first be a caterpillar... or a bug... or something like that.
I loved TrevorLaws butterflys so much (even though mine failed) that I wanted to do a vertsion with eyes... and feet.
First you'll need butterfly (or body) segments, so head over to TrevorLaws butterfly and get that: http://www.thingiverse.com/thing:11369
You'll want to print 2 of them for a bug, or 4 (or more if you dare!) for a caterpillar.
Then print twice the number of feet (4 for bug, 8 caterpillar).
Finaly print two eyes... they are not well made for printing so you'll need support (I also liked the texture the support left on the eye and didn't need to file it back).
Russel up about 5~10m of 5mm vinyl. Then assemble... easy as pie :) (this part may not be so easy). The easyest way I found was to glue up the left half, then fill with liquid, then glue up the other half. Good luck.
Oh, and I made mine in ABS... if you're going to give it to kids you should probably use PLA.
P.S. I colored in the eyes with texta :p