I think in the musical they have a little bit more singing in Matchmaker - they get to sing in group parts and I think have a couple of solo lines each (though I don't remember entirely because they had them sing both sets of lines as a duet in our production...plus it was nearly 10 years ago!
) They also have a couple of lines. I remember Shprintze says 'Can I go outside and play?' and Bielke says 'Can I go too?'. I think I can also recall Bielke saying 'Papa's home!'. They also have a fair bit of stage time, mainly playing games and running around a giggling. Plus they're in songs like Tradition, Sabbath Prayer, Sunrise Sunset and Anatevka. Plus there is the scene towards the end when Yente finds matches for them.
I kind of doubt that an 11 year old could do Chava. Firstly, she needs to seem older than Shprintze and Bielke - so they would have to cast very young kids for that to be the case! Secondly, she has to be old enough for it to be believable for her to fall in love. The idea of Yente finding husbands for the two little girls is supposed to be ridiculous - but Chava is genuinely in love. I don't think that would be believable from an 11 year old. Also, Chava is quite a demanding role acting-wise. She has one scene in particular that I think would need a lot more maturity than an 11 year old could deliver (no offence!
). Finally, I think it's usually preferably to cast older people rather than kids (as they're usually more mature, experienced, have better attention spans, etc.).