Hopefully they use children...
in the first script of suspiria, dario had originally intended to use very little girls, such as those aging from 8-10 years of age, but ended up changing it due to producer issues. if you watch the infamous hallway scene in the early part of the film (where suzy encounters the maid and albert--a kid which i do find scary), notice the door handles are placed up higher, nearly at head-height of suzy. this was to give an appearance of someone smaller.
i'm not particularly for this remake, but if they do, and it seems they are, i would hope they would try it from the original standpoint, and try to keep as much to the original as possible (like the soundtrack, decor, and design)
and hopefully, the girls will not have attitude like you see so much in cinema nowadays. it's hard to feel bad for a person you hate, whereas you end up anticipating their demise....
anyway! that's my two cents on the matter