Yes, I know about Wild Kratts - my son is always pretending to put a creature power disc into his baby brother and me! If the girls are just coming for dinner, do they need creature power vests? Maybe everyone can get their vests after dinner is over (and the older girls leave)? Otherwise, both of the girls on the show wear headbands or ponytails.
IF you didn't already see this blog post on another wild kratts bday party you might find it helpful: http://4teamplayers.blogspot.com/2011/06/abrams-6th-birth...
Good luck! C.