Just a quick question

My babies are 2 months old and although they´re my 4th and 5th yorkies,I cant remember when the ears are supposed to stand up right now..
The thing is,their ears seem to stand one day,and totally flop the next,and sometimes Im worried that they´ve hurt them selfs whilst playing or something (they tug each others ears).
Everyone keeps telling us "OMG dont touch their ears EVER or they´ll never stand"..but these pups can be rough and they seem to drag each other around by them
I cant remember if my previos babies went through up and down stages,so could someone please refresh my memory?
Floppy one day and almost up the next..is this ok?
Thank you in advance