all i can say is watch there feed ..young birds are very good liers.....it wont ert to get em hungery for one day.when they know they can fly in open air they will.
but try to get em to walk the garden first...when some get air born and head strong,your numbers may decline and end up paying big courier bills...
if your worried about fly aways you can always soap them up.
all the best mate good luck