The girls will most liklye be roataing days, they will prob each do 4 but then still have to be there for the start of the show for the 4 they are not one. A lot of time they don't need to alternate the kids if there not on stage a lot, like for Tazan and Chip they didn't HAVE to, they do so that one kid doens't sit back stage all the time its hard for a kid. Abby who was the girls u/s for both girls in Grey Gardens was miserable a lot of the time having to hang out and not go on much until towards the end. She used to come hang with us in the merch areas.
So marry Poppins has to have more then one cast of children becasue they are one stage pretty much the whole show but Tarzan Didn't because they where on stage for like 20 min if that a night. If one of the kids went on vacation or something the other kid could do the whole week and it would still be ok, thats why there are 3 cast for marry Poppins becasue one kid can't do the whole week by law.
Grace: My love for you is like this scar (points to elbow) ulgy but permanent!